ME ENGINES an article

Preamble

In the field of research and development of marine two stroke diesel engine it was a decade of remarkable landmarks. Camshaft-controlled diesel engines have been the state of the art ever since the birth of reciprocating machinery and have been refined and developed ever since. However, a mechanical cam is fixed once made and, in spite of various mechanical and hydraulic add-on devices like VIT, etc., timing control possibilities are limited with mechanical cams. Not least fuel injection pressure control and variation over the load range have limitations with a camcontrolled engine.

Therefore, the main purpose of changing to electronic control is to ensure fuel injection timing and rate, as well as the exhaust valve timing and operation, exactly when and as desired.

Especially with respect to the fuel injection rate, the control system has been so designed that it is possible to maintain a rather high injection pressure also at low load, without the limitation from the camshaft-controlled engine, where this would result in too high pressure at high load. Both the ‘cam angle, inclination and length’ are electronically variable.

The major competitors in marine diesel engines like Wartzila NSD, MAN B & W  and Mitsubishi UEC have developed revolutionary models with principle differeces of their design  and operational concepts are compared in the following chapters

ME Engines – the New Generation of Diesel Engines

INTRODUCTION

The electronic control of the engine fuel injection and exhaust valves improves low-load operation, engine acceleration, and give better engine balance and load control, leading to longer times between overhauls, also by implementation of enhanced diagnostics systems. It will give lower fuel consumption, lower cylinder oil consumption and, not least, better emission characteristics, particularly with regard to visible smoke and NOx, see Fig. 3 for a summary.

The ME engine features electronic control of the cylinder lube oil feed, by having our proprietary Alpha Lubricators integrated in the system. With the Alpha Lubrication system, about 0.3 g/bhph cyl. oil can be saved, compared with engines with mechanical lubricators.

For the ME engines, the electronic control system has been made complete. Hence, the ME engine features fully integrated control of all functions like the governor, start and reversing, fuel, exhaust and starting valves, as well as cylinder oil feeding, as  summarised in Fig. 4.

ELEMENTS OF THE ME-C ENGINE

The mechanical difference between an MC-C engine and its electronically controlled counterpart, the ME-C engine, constitutes a number of mechanical parts made redundant and replaced by hydraulic and mechatronic parts with enhanced functions, as illustrated in Fig. 5 and summarised below:

The following parts are omitted:

·         Chain drive

·         Chain wheel frame

·         Chain box on frame box

·         Camshaft with cams

·         Roller guides for fuel pumps and exhaust valves

·         Fuel injection pumps

·         Exhaust valve actuators

·         Starting air distributor

·         Governor

·         Regulating shaft

·         Mechanical cylinder lubricator

·         Local control stand

The above-mentioned parts are replaced by:

·         Hydraulic Power Supply (HPS)

·         Hydraulic Cylinder Units (HCU)

·         Engine Control System (ECS), controlling the following:

Ø  Electronically Profiled Injection (EPIC)

Ø  Exhaust valve actuation

Ø  Fuel oil pressure boosters

Ø  Start and reversing sequences

Ø  Governor function

Ø  Starting air valves

Ø  Auxiliary blowers

·         Crankshaft position sensing system

·         Electronically controlled Alpha Lubricator

·         Local Operating Panel (LOP)

Fig. 6 shows how the necessary power for fuel injection and exhaust valve operation – previously provided via the chain drive – is now provided from a Hydraulic Power Supply (HPS) unit located at the front of the engine at bedplate level.

 The main components of the Hydraulic Power Supply unit are the following:

·         Self cleaning filter with 10-micron filter mesh

·         Redundancy filter with 25-micron filter mesh

·       Start up pumps:  High-pressure pumps with supply pressure of 175 bar

  Low-pressure pumps for filling the exhaust valve push rod with supply

pressure of 4 bar

·         Engine driven axial piston pumps supplying high pressure oil to the Hydraulic Cylinder  Unit with oil pressures up to 250 bar.

Before engine start, the hydraulic oil pressure used in the mechanical/hydraulic system (for controlling the actuators) is generated by electrically driven start-up pumps. After start, the engine driven pump will take over the supply.

The engine driven pumps are gear or chain driven, depending on engine size. If so preferred, all pumps can also be electrically driven. The hydraulic pumps are axial piston pumps with flow controlled by the integrated control system. There are three engine driven pumps, but actually only two are needed for operation. Second-order moment compensators, where needed, can be integrated into the pump drive. Alternatively, electrically driven compensators can be used. If so preferred, the entire hydraulic oil system can be made as a separate, independent system.

Fig. 7 shows the entire hydraulic oil loop with the hydraulic power supply system and, as can be seen, the generated servo oil is fed via double-walled piping to the Hydraulic Cylinder Units of which there is one per cylinder, mounted on a common base plate on the top gallery level on the engine, as illustrated in Fig. 8 and detailed in Fig. 9. In this latter image, also the important electronic control valves, i.e. the ELFI (a proportional ELectronic Fuel Injection control valve) and the ELVA (an on-off Electronic exhaust Valve Actuator) are shown.

The Hydraulic Cylinder Unit furthermore comprises a hydraulic oil distribution block withpressure accumulators, the exhaust valve actuator, with ELVA and a fuel oil pressure booster with ELFI, raising the fuel oil supply pressure during injection from the 10-bar supply pressure to the specified load-dependent injection pressure of 600-1000 bar. Permanent high pressure with preheated fuel oil on top of the engine is thereby avoided, without losing any advantage of highpressure injection.

Figs. 10 and 11 show the per cylinder fuel oil injection system, and Fig. 12 shows theindividual components of the fuel oil pressure booster. As will appear, the fuel oil pressure booster is mechanically much more simple than the traditional fuel pump with roller, roller guide, VIT and cut-off wedges. Figs. 12 and 13 outline the media and plunger movements in respect to a signal to the ELFI from the engine control system, Fig. 14 shows the impeccable condition of the parts after about 4,000 hrs. of operation. Now more than 10,000 hrs have been logged, and the results are still the same. There has been virtually nothing to report. The fuel oil pressure booster is less exposed to wear than a traditional fuel oil pump and, with its significantly larger sealing length (compared with the conventional Bosch-type fuel pumps), a much longer lifetime can be expected.

Fig. 15 explains in detail how the actuator for the exhaust valve responds to the electronic actuator signal from the engine control system.

Another system that benefits from mechanical simplification by being electronically rather than mechanically controlled on the ME engine is the starting air system, Fig. 16. The mechanical starting air distributor is past history.

The Alpha Lubricator system for cylinder oil feed rate control, already with more than 200 sets sold, benefits in the ME engine version by using the 200-bar servo oil pressure as driving force rather than a separate pump station used in the stand-alone systems. The ME execution, therefore, as illustrated in Fig. 17, separates the cylinder oil from the servo oil. As shown in Fig. 18 (and Fig. 7), the Alpha Lubricator is mounted on the hydraulic oil distribution block. he ME engine control system, simplified in Fig. 19 and with more details in Fig. 20, is designed with the principle that no single failure of anything shall make the engine inoperative. Therefore, all essential computers are with a hot stand-by.

All the computers in the system, referred to as Engine Interface Control Unit, Engine Control Units, Cylinder Control Units and Auxiliary Control Units, are of exactly the same execution and can replace each other, in that they will adapt to the desired functionality of the particular location once installed, including if replaced by a spare. The computer, often referred to as a Multi-Purpose Controller, is a proprietary in-house development of MAN B&W Diesel. Thus, we can ensure spare part deliveries over the engine’s lifetime. The Local Operating Panel, incl. Cylinder Control and Auxiliary Control Units, see Fig. 21, is mounted on the middle gallery of the 7S50ME-C made in  Denmark. The Control Units can, of course, also be located elsewhere.

As to installation aspects, Fig. 22 illustrates that, apart from the cabling of the control network, an ME-C engine and an MC-C engine are practically the same for a shipyard, as detailed below:

·         Overhaul height: same

·         Engine seating: same

·         Engine outline: modifications with no influence for yard

·         Engine weight: slightly reduced

·         Engine pipe connection: back flush from filter on engine added, other connections

are unchanged

·         Gallery outline: slight modifications

·         Top bracing exhaust side: same

·         Capacity of auxiliary machinery: same

·         Lubricating oil system: slightly modified

·         Specification and installation of governor omitted

·         Other systems: same

·         Cabling: cables added for communication and network

Actually, there is a small simplification, as illustrated in Fig. 23, in that the tooling for the exhaust valve system and fuel oil pressure booster system is simpler.

FEATURES OF THE ME-C ENGINE

As mentioned in the introduction, the purpose of making electronic engines is focused around the virtues related to “ensuring fuel injection and rate, as well as exhaust valve timing exactly when and as desired”.

With respect to the exhaust valve movement, this means changing the ‘cam length’, asillustrated in Fig. 24, by simply changing the point in time of activating the ELVA valve . This can be used to control the energy to the turbocharger, both during steady and transient load conditions. Smoke-free acceleration is a natural benefit apart from SFOC optimization at any load. Fig. 25 gives an illustration of how already a ‘different cam length’ was implemented on the 7S50ME-C engine in Frederikshavn for 100% load vs. 75% load.

Thanks to the multitude of possibilities with the ELFI, the proportional valve controlling the servo oil pressure to the fuel oil pressure booster, not only the fuel oil ‘cam length’, but also the ‘cam inclination and angle’ and even the number of activations per stroke can be varied for the fuel oil injection.

Fig. 26 illustrates different profiles demonstrated during testing of the 7S50ME-C. The double injection profile is specially tailored for a significant reduction of NOxemissions as referred to later (see Fig. 32).

Fig. 27 shows the selected injection rate on that engine at 75% load, compared with what it would have been with a fixed cam. The resulting heat release, see Fig. 28, is the reason for selecting a more intensive injection. A better heat release mirrors a better fuel consumption, also because the pmax is higher, see Fig. 29. Such data could of course also be realised on a mechanical engine, but not while at the same time maintaining the ability to perform at 100% load. In the low end of the load scale, the possibility for controlling the timing and rate of injection gives the possibility to demonstrate stable running down to 10% of MCR-rpm, i.e. 13 rpm against a

water brake only. This could be even more stable against a propeller eliminating the need for stop-and-go operation through channels and canals and making ME engines particularly suitable for shuttle tankers and lightering vessels, as well as for vessels with greatly varying load profile.

General performance curves for the ME-C and MC-C engines are shown in Fig. 30. The lower part load fuel consumption is achieved by raising the pmax over the whole load range. In order to avoid too high difference between pmax and pcomp, also this pressure is raised by timing control.

As also illustrated, the lower SFOC comes at a price in that the NOx increases. For this reason, the first two modes to be incorporated in the control system of the ME engine, as standard, are the ‘fuel economy mode’ and the ‘low-NOx’ mode. Fig. 31 illustrates the coagency between SFOC, NOx, and pmax/Pcomp for the two modes.

It goes without saying that an ME-C engine will comply with IMO’s NOx cap also in the fuel economy mode.

The low-NOx mode is intended for areas where lower than IMO NOx limits do or will apply.

The change from one mode to the other is a matter of seconds only and, of course, is done while running, as illustrated in Fig. 32.

SUMMARY

The advantages of the ME-C range of engines are quite comprehensive, as seen below:

·         Lower SFOC and better performance parameters thanks to variable electronically

            controlled timing of fuel injection and exhaust valves at any load

·         Appropriate fuel injection pressure and rate shaping at any load

·         Improved emission characteristics, with lower NOx and smokeless operation

·         Easy change of operating mode during operation

·         Simplicity of mechanical system with wellproven traditional fuel injection technology familiar to any crew

·         Control system with more precise timing, giving better engine balance with equalized thermal load in and between cylinders

·         System comprising performance, adequate monitoring and diagnostics of engine for longer time between overhauls

·         Lower rpm possible for manoeuvring

·         Better acceleration, astern and crash stop performance

·         Integrated Alpha Cylinder Lubricators

·         Up-gradable to software development over the lifetime of the engine

It is a natural consequence of the above that many more features and operating modes are feasible with our fully integrated control system and, as such, will be retrofittable and eventually offered to owners of ME-C engines.

Against this background, we are proud to present our ME-C engine programme, as

shown in Fig. 33.

All figures mentioned above is given below

Fig. 1: 7S50ME-C, MAN B&W Diesel, Denmark, February 2003

Fig. 2: Electronically Controlled Engines, precise control

Fig. 3: Electronically Controlled Engines, improved features

Fig. 4: Electronically Controlled Engines, fully integrated control

Fig. 5: From MC-C to ME-C – Mechanical Differences

Fig. 6: Hydraulic Power Supply (HPS)

Fig. 7: ME-C Engines, Hydraulic Oil Loop

Fig. 8: Hydraulic Cylinder Units (HCU)

Fig. 9: Hydraulic Cylinder Unit (HCU)

Fig. 10: Fuel Injection System

Fig. 11: Fuel Injection System

Fig. 12: Fuel Oil Pressure Booster

Fig. 13: Fuel Oil Pressure Booster

Fig. 14: Fuel Oil Pressure Booster Actuator

Fig. 15: Exhaust Valve Actuator

Fig. 16: ME Starting Air System

Fig. 17: Alpha Lubricator for ME Engine

Fig. 18: Alpha Lubricator System for ME

Fig. 19: ME Engine Control System

Fig. 20: Configuration of Control System

Fig. 21: Local Operating Panel (LOP)

Fig. 22: Installation Aspects, ME Engine

Fig. 23: ME – Maintenance Aspects

Fig. 24: Exhaust Valve Timing

Fig. 25: Exhaust Valve Closing Time

Fig. 26: Injection Profiles

Fig. 27: Injection at 75% load, ME-C versus MC-C

Fig. 28: Heat Release at 75% load, ME-C versus MC-C

Fig. 29: Cylinder Pressures at 75% load, ME-C versus MC-C

Fig. 30: Performance Curves, ME-C versus MC-C

Fig. 31: Performance Curves, Economy versus low-NOx

Fig. 32: 7S50ME-C – 75% load

Fig. 33: ME Engine Programme

chapter-2

The Intelligent Engine concept

ADVANTAGES

Ø  on-line monitoring ensures uniform load distribution among cylinders

Ø  an active on-line overload protection system prevents thermal overload

Ø  early warning of faults under development, triggering countermeasures - significantly improved low load operation.

• Enhanced emission control flexibility:

Ø  emission performance characteristics optimised to meet local demands

Ø   later updating possible.

• Reduced fuel and lube oil consumption:

Ø  engine performance fuel-optimised at ‘all’ load conditions

Ø  ‘as new’ performance easily maintained over the engine lifetime

Ø  mechatronic cylinder lubricator with advanced dosage control.

The Intelligent Engine Concept

To meet the operational flexibility target, it is necessary to have great flexibility in the operation of – at least – the fuel injection and exhaust valve systems. Achieving this objective with cam-driven units would require substantial mechanical complexity that would hardly contribute to engine reliability.

To meet the reliability target, it is necessary to have a system that can protect the engine from damage due to overload, lack of maintenance, mal-adjustment, etc. A condition monitoring system must be used to evaluate the general engine condition so as to maintain the engine performance and keep its operating parameters within the prescribed limits and to keep it up to ‘as new’ standard over the lifetime of the engine.

The above indicates that a new type of drive has to be used for the injection pumps and the exhaust valves and that an electronic control and monitoring system will also be called for. The resulting concept is illustrated in Fig. 1.

The upper part shows the Operating Modes which may be selected from the bridge control system or by the intelligent engine’s own control system. The control system contains data for optimal operation in these modes, which  consist of a number of single modes corresponding, for instance, to different engine loads and different required emission limits.

The fuel economy modes and emission controlled modes (some of which may incorporate the use of an SCR catalytic clean-up system) are selected from the bridge. The optimal reversing/crash stop modes are selected by the electronic control system itself when the bridge control system requests the engine to carry out the corresponding operation.

The engine protection mode is, in contrast, selected exclusively by the condition monitoring and evaluation system, regardless of the current operating mode. Should this happen in circumstances where, for instance, reduced power is unacceptable for reasons of the safety of the ship, the protection mode can be cancelled from the bridge.

The centre of Fig.1 shows the brain of the system: the electronic control system. This analyses the general engine condition and controls the operation of the following engine systems (shown in the lower part of Fig. 1): the fuel injection system, the exhaust valves, the cylinder lubrication system and the turbo charging system.

Some of the control functions for these units are, as mentioned above, pre-optimised  and can be selected from the bridge. Other control functions are selected by the engine condition monitoring system on the basis of an analysis of various input from the units on the left and right sides of Fig. 1: general engine performance data, cylinder pressure, cylinder condition monitoring data and output from the Load Control Unit. More detailed descriptions of these systems can be found in Ref. [1].

Fig. 1: The Intelligent Engine concept

The Condition Monitoring and Evaluation System is an on-line system with automatic sampling of all “normal” engine performance data, supplemented by cylinder pressure measurements, utilising our CoCoS-EDS system. When the data-evaluation system indicates normal running conditions, the system will not interfere with the normal pre-determined optimal operating modes. However, if the analysis shows that the engine is in a generally unsatisfactory condition, general countermeasures will be initiated for the engine as a unit. For instance, if the exhaust gas temperature is too high, fuel injection may be retarded and/or the exhaust valves may be opened earlier, giving more energy to the turbocharger, thus increasing the amount of air and reducing the exhaust gas temperature.

At all events, the system reports the unsatisfactory condition to the operator together with a fault diagnosis, a specification of the countermeasures used or proposed, and recommendations for the operation of the engine until normal conditions can be re-established or repairs can be carried out. The 4T50MX research engine in our R&D Centre in Copenhagen was operated from 1993 to 1997 with the first-generation Intelligent Engine (IE) system. The engine has been running with this system for the IE development as well as for its normal function as a tool for our general engine

Fig. 2: Second-generation ‘Intelligent Engine’ system fitted to the 4T50MX research engine in 1997

development. The 1990 running hours logged during that period of time has provided us with significant experience with this system. Being the first generation of IE, the system was somewhat ‘over-engineered’ and relatively costly compared with the contemporary camshaft system. On the other hand, the system offered much greater flexibility, which has proved its value in the use of the research engine as one of our most important development tools.

In 1997, the engine was fitted with second-generation IE systems, please refer to Fig. 2 showing the fuel injection and exhaust valve actuating systems on the engine. The second-generation systems, to be described in more detail in the following, have been developed in order to:

• simplify the systems and tailor them to the requirements of the engine

• facilitate production and reduce the costs of the IE system

• simplify installation and avoid the use of special systems wherever possible.

On the electronic software/hardware side, the original first-generation system was used for a start. Since then, significant development efforts have been invested in transforming the electronic part of the IEsystem into a modular system, where some of the individual modules can also be used in conventional engines. This means development of a new computer unit and large software packages – both of which have to comply with the demands of the Classification Societies for marine applications.

Design Features of the Second-Generation IE System

General description

The principle layout of the new system, replacing the camshaft system of the conventional engine, is illustrated in Fig. 3. The system comprises an enginedriven high-pressure servo oil system, which provides the power for the hydraulically operated fuel injection and exhaust valve actuation units on each cylinder. Before the engine is started, the hydraulic power system (or servo oil system) is pressurised by means of a small electrically driven high-pressure pump.

Furthermore, the starting air system and the cylinder lubrication system have been changed compared with the conventional engine series. A all these units.

The following description will outline the main features of these systems, together with our recent development work and experience.

Power supply system

Engine-driven multi-piston pumps supply high-pressure lube oil to provide the necessary power for fuel injection and exhaust valve actuation and thus replace the camshaft power-wise. The multi-piston pumps are conventional, mass-produced axial piston pumps with proven reliability.

The use of engine system oil as the activating medium means that a separate hydraulic oil system is not needed, thus extra tanks, coolers, supply pumps and a lot of piping etc. can be dispensed with. However, generally the engine system oil is not clean enough for direct use in high-pressure hydraulic systems, and it might be feared that the required 6 µm filter would block up quickly.

We have undertaken quite extensive development work in collaboration with a filter supplier (B&K) in order to ensure the cleanliness required for such systems – the very positive long-term results are described below.

Against this background, and based on the fact that the clean lube oil from the engine was at least as suitable for use in the hydraulic system as conventional hydraulic oil, we decided to base our system on fine-filtered system lube oil.

This is supplied from the normal system oil pumps, providing a higher inlet pressure to the high-pressure pumps than otherwise – this being yet another benefit.

Fig. 3: System diagram for the hydraulic flow (servo oil system)

Fuel injection system, design features

The general design of the system is shown in Fig. 4. A common rail servo oil system using pressurised cool, clean lube oil as the working medium drives the fuel injection pump. Each cylinder unit is provided with a servo oil accumulator to ensure sufficiently fast delivery of servo oil in accordance with the requirements of the injection system and in order to avoid heavy pressure oscillations in the associated servo oil pipe system.

Fig. 4: General system layout for fuel injection and exhaust valve actuation systems

The movement of the plunger is controlled by a fast-acting proportional control valve (a so-called NC valve), developed by our cooperation partner Curtiss Wright Drive Technology GmbH (formerly known as SIG Antriebstechnik) of Switzerland.  The NC valve is, in turn, controlled by an electric linear motor that gets its control input from the cylinder control unit (see below).

This design concept has been chosen in order to maximise reliability and functionality – after all, the fuel injection system is the heart of the engine, and its performance is crucial for fuel economy, emissions and general engine performance. An example of the flexibility of the fuel injection system will be given below.

The key components have a proven reliability record: the NC valves have been in serial production for some ten years and are based on high-performance valves for such purposes as machine tools and sheet metal machines in car production – applications where high reliability is crucial. The fuel njection pump features well-proven fuel injection equipment technology, and the fuel valves are of our well-proven and simple standard design.

As can be seen in Fig. 5, the 2nd and 3rd generations of pump design are substantially simpler than  he 1st generation design, the components are smaller, and they are very easy to manufacture. By mid-2000, the 2nd generation pump had been in operation on the 4T50MX research engine for more than 1400 hours, whereas the 3rd generation is starting service testing on the 6L60MC (see below)

The major new design feature for the 3rd generation pump is its ability to operate on heavy fuel oil.  he pump plunger is equipped with a modified umbrella design to prevent heavy fuel oil from entering the lube oil system. The driving piston and the injection plunger are simple and are kept in contact by the fuel pressure acting on the plunger, and the hydraulic oil pressure acting on the driving piston. The beginning and end of the plunger stroke are both controlled solely by the fast acting hydraulic valve (NC valve), which is computer controlled.

Fig. 5: Design development of fuel injection pumps

Fuel injection system, rate shaping capability

The optimum combustion (thus also the optimum thermal efficiency) requires an optimised fuel injection pattern which is generated by the fuel injection cam shape in a conventional engine. Large two-stroke engines are designed for a specified max. firing pressure, and the fuel injection timing is controlled so as to reach that firing pressure with the given fuel injection system (cams, pumps, injection nozzles, etc.).

For modern engines, the optimum injection duration is around 18-20 degrees crank angle at full load, and the max. firing pressure is reached in the second half of that period. In order to obtain the best thermal efficiency, fuel to be injected after reaching the max. firing pressure must be injected (and burnt) as quickly as possible in order to obtain the highest expansion ratio for that part of the heat released.

From this it can be deduced that the optimum ‘rate shaping’ of the fuel injection is one showing  increasing injection rate towards the end of injection, thus supplying the remaining fuel as quickly as possible. This has been  proven over many years of fuel injection system development for our two-stroke marine diesel engines, and the contemporary camshaft is designed accordingly.

The fuel injection system for the Intelligent Engine is designed to do the same but in contrast to the camshaft- based injection system, the IE system can be optimised at a large number of load conditions.

Fig. 6: Comparison between the fuel injection characteristics of the ME engine and a Staged Common Rail system in terms of injection pressure, mass flow rate and flow distribution

Common Rail injection systems with on/off control valves are becoming standard in many modern diesel engines at present. Such systems are relatively simple and will provide larger flexibility than the contemporary camshaft based injection systems. We do apply such systems for controlling the high-pressure gas-injection in the dual-fuel version of our MC engines, where the (two-circuit)  common rail system provides the necessary flexibility to allow for varying HFO/gas-ratios, please refer to [3].

Fig. 7: Fuel spray distribution in the combustion chamber (schematically) corresponding to the injection patterns illustrated in Fig. 6

However, by nature the common rail system provides another rate shaping than what is optimum for the engine combustion process. The pressure in the rail will be at the set-pressure at the start of injection and will decrease during injection because the flow out of the rail (to the fuel injectors) is much faster than the supply of fuel into the rail (from high-pressure pumps supplying the average fuel flow).

As an example, an 8-cylinder engine will have a total ‘injection duration’ per engine revolution of 160 deg. CA (8 x 20 degrees CA) during which the injectors supply the same mass flow as the high-pressure supply pumps do during 360 deg. CA. Thus, the outflow during injection is some 360/160 = 2.25 times the inflow during the same period of time. Consequently, the rail pressure must drop during injection, which is the opposite of the optimum rate shape. To counteract this, it has been proposed to used ‘Staged Common Rail’ whereby the fuel flow during the initial injection period is reduced by opening the fuel valves one by one.

The Rate Shaping with the IE system (using proportional control valves) and the ‘Staged Common Rail’ are illustrated in Fig. 6. This shows the injection pressure, the mass flow and the total mass injected for each fuel valve by the two systems, calculated by means of our advanced dynamic fuel injection simulation computer code for a large bore engine (K98MC) with three fuel valves per cylinder. In the diagram, the IEsystem is designated ME(this being the engine designation, like 7S60ME-C). As can be seen, the Staged Common Rail system supplies a significantly different injection amount to each of the three fuel valves.

Fig. 8: Four examples of fuel injection pressures at the fuel valve, and the corresponding fuel valve spindle lifting curves

Fig. 9: Effect of injection pattern on combustion rate, NOx emission and specific fuel oil consumption (test on 4T50MX research engine at 75% load)

Though the Staged Common Rail system will provide a fuel injection rate close to the optimum injection rate, combustion will not be optimal because the fuel is very unevenly distributed in the combustion chamber whereas the combustion air is evenly distributed. This is illustrated (somewhat overexaggerated to underline the point) in Fig. 7: the valve opening first will inject the largest amount of fuel and this will penetrate too much and reach the next fuel valve nozzle.

Experience from older engine types indicates that this may cause a reliability problem with the fuel nozzles (hot corrosion of the nozzle tip).  The uneven fuel injection amount means that there will be insufficient air for the fuel from the first nozzle, the correct amount for the next and too much air for the third fuel valve. The average may be correct but the result cannot be optimal for thermal efficiency and emissions. Uneven heat load on the combustion chamber components can also be foreseen - though changing the task of injecting first among the three valves may ameliorate this.

Thus, the IE injection system is superior to any Common Rail system – be it staged or simple.  Extensive testing has fully confirmed that the IE fuel injection system can perform any sensible injection pattern needed for operating the diesel engine. The system can perform as a single-injection system as well as a pre-injection system with a high degree of freedom to modulate the injection in terms of injection rate, timing, duration, pressure, single/double injection, etc. In practical terms, a number of injection patterns will be stored in the computer and selected by the control system so as to operate the engine with optimal injection characteristics from dead slow to overload, as well as during astern running and crash stop. Change-over from one to another of the stored injection characteristics may be effected from one injection cycle to the next.

Some examples of the capability of the fuel injection system are shown in Fig. 8. For each of the four injection patterns, the pressure in the fuel valve and the needle-lifting curve are shown. Tests on the research engine with such patterns (see Fig. 9) have confirmed that the ‘progressive injection’type (which corresponds to the injection pattern with our optimised camshaft driven injection system) is superior in terms of fuel consumption. The ‘double injection’ type gives slightly higher fuel  consumption, but some 20% lower NOx emission – with a very attractive trade-off between NOx reduction and SFOC increase.

Fig. 10: Hydraulic cylinder unit with fuel injection pump and exhaust valve actuator

Exhaust valve actuation system

The exhaust valve is driven by the same servo oil system as that for the fuel injection system, using pressurised cool, clean lube oil as the working medium. However, the necessary functionality of the exhaust valve comprises only control of the timing of opening and closing the valve. This can be obtained by using a simple fast-acting on/off control valve.

The system features well-proven technology from the present engine series. The actuator for the exhaust valve system is of a simple two-stage design, please refer to Fig. 10. The first-stage actuator piston is equipped with a collar for damping in both directions of movement. The second-stage actuator piston has no damper of its own, and is in direct contact with a gear oil piston transforming the hydraulic system oil pressure into oil pressure in the oil push rod. The gear oil piston includes a damper collar that becomes active at the end of the opening sequence, when the exhaust valve movement will be stopped by the standard air spring.

Control system

Redundant computers connected in a network provide the control functions of the camshaft (timing and rate shaping) - please refer to Fig. 11. This new  Engine Control System (see also [2]) is an integrated part of the Intelligent Engine that brings completely new characteristics to the engine. It comprises two Engine Control Units (ECU), a Cylinder Control Unit (CCU) for each cylinder, a Local Control Terminal and an interface for an external Application Control System. The ECU and the CCU have both been developed as dedicated controllers, optimised for the specific needs of the intelligent engine.

The Engine Control Unit controls functions related to the overall condition of the engine. It is connected to the Plant Control System, the Safety System and the Supervision & Alarm System, and is directly connected to sensors and actuators. The function of the ECU is to control the action of the following components and systems:

Fig. 11: Control system for the Intelligent Engine

The engine speed in accordance with a reference value from the application control system (i.e. an integrated governor control)

• Engine protection (overload protection as well as faults)

• Optimisation of combustion to suit the running condition

• Start, stop and reversing sequencing of the engine

• Hydraulic (servo) oil supply (lube oil)

• Auxiliary blowers and turbocharging.

The Cylinder Control Unit is connected to all the functional components to be controlled on each cylinder. Its function  is to control the activation of features like:

• Fuel injection

• Exhaust valve

• Starting valve

• Cylinder lubricator for the specific cylinder.

As faults can never be completely ruled out, even with the best design of electronic (or mechanical) components, the concept for the intelligent engine has been designed with great care regarding fault tolerance and easy repair, to ensure the continuous operation of the ship. Since each cylinder is equipped with its own controller (the CCU), the worst consequence of a CCU failure is a temporary loss of power from that particular cylinder (similar to, for instance, a sticking fuel pump on a conventional engine). The engine controller (ECU) has a second ECU as a hot stand-by which, in the event of a failure, immediately takes over and continues the operation without any change in performance (except for the decreased tolerance for further faults until repair has been completed).

In the event of a failure in a controller, the system will identify the faulty unit, which is simply to be replaced with a spare. As soon as the spare is connected, it will automatically be configured to the functions it is to replace, and resume operation. As both the ECU and the CCU are implemented in the same type of hardware, only a few identical spares are needed. If failures occur in connected equipment – sensors, actuators, wires, etc. – the system will locate the area of the failure and, through built-in guidance and test facilities, assist the engine operating staff in the final identification of the failed component.

Cylinder pressure measuring system (PMI)

A reliable measurement of the cylinder pressure is essential for ensuring ‘as new’ engineer formance. A conventional mechanical indicator in the hands of a skilled and dedicated crewmember can provide reasonable data. However, the necessary process is quite time consuming and the cylinder pressure data obtained in this way is not available for analysis in a computer, which means that some valuable information is less likely to be utilised in a further analysis of the engine condition. A computerized measuring system with a high quality pressure pick-up connected to the indicator bore may provide this. We have developed such a system, PMI Off-Line, of which more than 100 sets have been sold for application on our conventional engines.

For the Intelligent Engine, on-line measurements of the cylinder pressure are necessary – or at least greatly desirable.  In this case, the indicator cock cannot be used since the indicator bore will clog up after a few days of normal operation, making further measurements useless.

Fig. 12: PMI on-line cylinder pressure sensor of the strain-pin type, built into the cylinder cover, without contact with the corrosive combustion gases

Since we realised this quite some time ago, we have been working on the development of a reliable system for longterm continuous cylinder pressure measurements. The first, successful, attempt involved the use of strain gauges on two cover studs on each cylinder, thus in fact using the cylinder cover itself as a ‘pressure transducer’. A long-term test was carried out on the main engine of a anish ferry about ten years ago, and the system provided us with stable measurements over a period of more than 10,000 operating hours.

However, there was some electrical noise in the signals, and we decided to use another system that had been introduced on the market in the meantime: the strain-pin type of pressure sensor. The pressure-sensing element is a rod located in a bottom-hole in the cylinder cover, in close contact with the bottom of the hole, close to the combustion chamber surface of the cylinder cover, as can be seen in Fig. 12. Thus, the sensor measures the deformation of the cylinder cover caused by the cylinder pressure without being in contact with the aggressive combustion products and without having any indicator bore that can clog up. The position of the sensor also makes it easier to prevent electrical noise from interfering with the cylinder pressure signal.

The pressure transducer of the off-line system is used for taking simultaneous measurements for alibrating the on-line system. By feeding the two signals into the computer in the calibration mode, a calibration curve is determined for each cylinder. The fact that the same, high-quality, pressure ransducer is used to calibrate all cylinders means that the cylinder-to-cylinder balance is not at all influenced by differences between the individual pressure sensors.

The on-line as well as the off-line system provide the user with unique assistance for keeping the engine performance up to ‘as new’ standard and reduce the workload of the crew. The systems automatically identify the cylinder being measured without any interaction from the person carrying out the measurement (because the system contains data for the engine’s firing order). Furthermore, compensation for the crankshaft twisting is automatic, utilising proprietary data for the engine design. If there is no such compensation, the mean indicated pressure will be measured wrongly and when it is used to adjust the fuel pumps, the cylinders will not have the same true uniform load after the adjustment although it may seem so. Twisting of the crankshaft may lead to errors in mean indicated pressure of some 5% if not compensated for!

Fig. 13: Example of PMI system output: cylinder balance table with recommended

adjustments

The computer carries out the tedious and time-consuming work of evaluating the ‘indicator card’ data which are now in computer files, and the cylinder pressure data can be transferred directly to our CoCoS-EDS Engine Diagnosis System for inclusion in the general engine performance monitoring. Furthermore, the result presented to the crew is far more comprehensive and comprises a list of the necessary adjustments, as illustrated in Fig. 13. These recommendations take into account that the condition of the non-adjusted cylinders changes when the adjustments are carried out. So it is not necessary to check the cylinder pressure after the adjustment.

Electronic cylinder lubricator

The concept of the new electronic cylinder lubricator is illustrated in Fig. 14. A pump station delivers lube oil to the lubricators at 45 bar pressure. The lubricators have a small piston for each lube oil quill in the cylinder liner, and the power for injecting the oil comes from the 45 bar system pressure, acting on a larger common driving piston as shown in Fig. 15. Thus, the driving side is a conventional common rail system, whereas the injection side is a high-pressure positive displacement system, thus giving equal amounts of lube oil to each quill and the best possible safety margin against clogging of single lube oil quills.

Fig. 14: System design of the electronic cylinder lubricator

Fig. 15: Cylinder lubricator unit, controlled by the computer and driven by 45 bar lube oil pressure

For the large bore engines, each cylinder has two lubricators (each serving half of the lube oil quills) and an accumulator, while the small bore engines (with fewer lube oil quills per cylinder) are served by one lubricator per cylinder. The pump station includes two pumps (one operating, the other on stand-by with automatic start up), a filter and coolers.

The lubricator can be delivered for our conventional engines in which case it is controlled by a  separate computer unit comprising a main computer, controlling the normal operation, a switchover unit and a (simple) back-up unit. A shaft encoder (which can be shared with a PMI system) supplies  the necessary timing signal in that case. When used on ‘Intelligent Engines’, these functions are integrated in the engine control computers and their shaft encoders.

The lubrication concept is intermittent lubrication – a relatively large amount of lube oil is injected for every four (or five or six, etc.) revolutions, the actual sequence being determined by the desired dosage in g/bhph. The injection timing is controlled precisely and – by virtue of the high delivery pressure – the lube oil is injected exactly when the piston ring pack is passing the lube oil quills, thus ensuring the best possible utilisation of the costly lube oil. This is illustrated in Fig. 16.

            Fig. 16: Pressure measured in cylinder lubricating oil quills, and timing of lube oil injection

The control computers have passed the necessary tests (E10), and the final approval by a number of Classification Societies took place in Copenhagen in April 2000, paving the way for largescale commercial deliveries. Production of the electronic hardware has started and the first commercial units are in service on K90MC/MC-C/MC-S and S90MC-C engines.

Prior to that, the system was tested in operation on a 7S35MC for more than two years with good results, and tests on a cylinder of a K90MC engine over some 12,000 service hours have given very satisfactory results, with low lube oil dosage (for more details, please see [4]).

Starting air system. On the Intelligent Engine, the pneumatic control system for the starting air valves has been replaced by an electronically controlled system with solenoid valves on the starting air valves, offering greater freedom and more precise control. The ‘slow turning’ function is maintained.

Advantages of the Intelligent Engine Concept

The electronic control of the fuel injection system and the exhaust valve operation means a number of advantages that are briefly listed below, categorized in three main groups.

Reduced fuel consumption:

• fuel injection characteristics can be optimised at many different load conditions whereas a  conventional engine is optimised for the guarantee load, typically at 90-100% MCR

• constant pmax in the upper load range can be achieved by a combination of fuel injection timing and variation of the compression ratio (the latter by varying the closing of the exhaust valve). As a result, the max. pressure can be kept constant over a wider load range without overloading the engine, leading to significant SFOC reductions at part load.

• the on-line monitoring of the cylinder process ensures that the load distribution among the cylinders and the individual cylinder’s firing pressure can be kept up to ‘as new’ standard, maintaining the ‘as new’ performance over the lifetime of the engine.

Operational safety and flexibility:

• the engine’s crash stop and reverse running performance is improved because the timing of exhaust valves and fuel injection can be optimal for these situations too

• ‘engine braking’ may be obtained, reducing the stopping distance of the vessel

• faster acceleration of the engine because the scavenge air pressure can be increased faster than normal by opening the exhaust valve earlier during acceleration

• dead slow running is improved significantly: the minimum r/min is significantly lower than for a conventional engine, dead slow running is much more regular, and combustion is improved thanks to the electronic control of fuel injection

• the electronic monitoring of the engine (based on our CoCoS-EDS system) identifies running  conditions which could lead to performance problems. Damage due to poor-ignition-quality fuel can be prevented by fuel injection control (pre-injection)

•the engine control system includes our on-line OPS-feature: Overload Protection System, which ensures that the engine complies with the load-diagram and is not overloaded (as is often seen in shallow waters and with ‘heavy propeller’ operation)

• maintenance costs will be lower (and maintenance easier) as a result of the protection against general overloading as well as overloading of single cylinders, and the ‘as new’ running conditions for the engine, which is further enhanced by the ability of the engine diagnosis system to give early  warning of faults, thus enabling proper countermeasures to be taken in due time.

Flexibility regarding exhaust gas emissions:

• the engine can change over to various ‘low emission modes’ where its NOx exhaust emission can be reduced below the IMO limits if desirable due to ‘local’ emission regulations

• by suitable selection of operating modes, the vessels may sail with lower exhaust gas emission within ‘special areas’ where this may be required (or be economical due to special harbour fee schemes) without having negative effects on the SFC outside such special areas.

Service Experience with the Intelligent Engine

The world’s first Intelligent Engine in service as the main propulsion engine for a merchant vessel is the 6L60MC of the chemical product carrier M/T Bow Cecil, which was delivered in October 1998 to the Norwegian owner Odfjell ASA by the Kværner Florø Yard in Norway.

Design of IE systems for M/T Bow Cecil

The engine was prepared for the IE systems during its production. The mechanical/ hydraulic components of the IE systems were fitted to the engine during its installation in the vessel at the yard. These systems are installed on the upper platform of the engine, in parallel with the conventional camshaft, as shown in Fig. 17.

Fig. 17: Installation of the IE fuel injection and exhaust valve control systems in parallel with

the conventional camshaft of the 6L60MC main engine of M/T Bow Cecil

With this set-up, it is possible to change over completely from the conventional system to the IE system, or vice versa, within some three hours, so there is full redundancy. Fig. 18 is a photo taken at the yard in 1998, showing the installation of the IE systems on the upper platform of the engine.

The power for operating the fuel injection system and the exhaust valves is supplied by a hydraulic powerpack. This comprises high-pressure axial piston umps, driven by the engine (see Fig. 19), together with electrically driven pumps, supplying oil pressure prior to starting the engine and controlling the oil flow during its operation. The working medium is fine filtered engine system oil, as described in detail below.

Service experience with IE systems on M/T Bow Cecil

The ordinary camshaft system was used on the sea trial in accordance with the original contract between the parties, and it has also been used during the first operating period of the vessel. During this time, the auxiliary systems have been put in operation and tested thoroughly. The following has been experienced with these systems prior to the operation as a complete ‘Intelligent Engine’:

Fig. 18: Installation of IE system on the upper platfrom of the 6L60MC main engine of M/T Bow Cecil

Fig. 19: Engine driven high-pressure pumps on the front end of the 6L60MC engine

Hydraulic oil conditioning system. The power medium employed for operating the fuel injection pumps and the exhaust valves is fine-filtered system oil from the engine, thus avoiding a separate hydraulic oil system with tanks, pumps, coolers, etc. The driving system utilises lube oil at a moderate working pressure (160–200 bar), but even so it is essential for ensuring a long lifetime of such hydraulic systems that the oil is clean, which requires ISO x/16/13.

However, the requirements for the engine system oil are not that strict – nor are they needed for the engine itself; therefore, the oil for the IE systems requires extra filtration. For this purpose we use an automatic 6-micron filter located in the supply line to the IE system from the main lube oil pipe of the engine. From a system point of view, this acts as by-pass filtration and thus, over time, will fine-filter the whole oil charge of the engine – obviously with the risk of clogging the filter.

Before deciding to use this system, we had tested it on our 4T50MX research engine with good results, confirming that filter clogging was not a problem and that the higher inlet pressure supplied to the hydraulic power supply unit (engine-driven axial piston pumps) was indeed an advantage for these pumps.

Subsequently, the filter system was fitted to a sister vessel to M/T Bow Cecil and service tested over a period of one year. The results were very satisfactory, again confirming that filter clogging was not a problem and that also the whole oil charge of the engine became significantly cleaner than before – an added benefit for the engine.

The fine-filtering system has also been in operation on M/T Bow Cecil ever since the sea trial. The ‘commissioning’ of the filter during the sea trial is illustrated in Fig. 20. The first operating hours during a sea trial must be expected to deliver rather high amounts of particles (i.e. a high filter load). However, it can be seen that back-flushing of the filter is not triggered by the permissible pressure drop across the filter (max. 0.6 bar) being exceeded, but only by the timer, which is set to backflush every hour. The subsequent service experience with the system has been very satisfactory – the only problem encountered was a ‘cold soldering’ on the print card for the filter control, which has been rectified by the supplier.

            Fig. 20: Commissioning of fine-filter during the sea trial of M/T Bow Cecil

On-line cylinder pressure measuring system PMI, and CoCoS-EDS.

 These two systems were installed on the engine in August 1999 and are now being used by the crew as normal tools for monitoring the engine. After some minor teething troubles onboard, the PMI system is working stable and reliably, providing on-line data on the working of the cylinders to the CoCoS Engine Diagnosis System (EDS).

Electronic hardware and software.

 The development of the electronic control systems for fuel injection and exhaust valve actuation was delayed due to the complexity of the software. The hardware has passed the required test (E10). Software approval is a two-step procedure: first, a SW development audit must be performed by the Classification Society in question (Det Norske Veritas). This has been done, and we have been approved for developing such software. The second step comprises a demonstration (on the 4T50MX research engine) of the functionality of the SW in the actual HW, for the purpose of proving that the complete system works as described in the design specification. This test was performed to the full satisfaction of DNV in September 2000.

The Mode Selection screen of the HMI (Human Machine Interface) is shown in Fig. 21. Using this, the operator has the possibility to switch between the operating modes for the engine (‘Fuel Economy’ and ‘Emission Control’), as well as to switch between governor control modes such as ‘Constant Speed’ and ‘Constant Torque’.

An overview of the engine status is available from the ‘Main Status Display’, as can be seen in Fig. 22. This shows (at the top) the actual mode for the engine, the governor and the hydraulic power supply system. It indicates from where control is taking place (the bridge in the case shown here) together with index status and the actual propeller pitch for the CP propeller.

Control of the hydraulic power supply. The control software for the hydraulic power supply (engine and electrically driven hydraulic pumps) has been finalized and tested. The control system was successfully installed and tested on board M/T Bow Cecil in April 2000.

Full scale IE service tests on M/T Bow Cecil. After completion of the demonstration of system functionality for DNV, the next step was to start actual operation with the computer controlled fuel injection and exhaust valve actuation systems – the world’s first full scale ‘Intelligent’ marine engine in service.

In consideration of the vessel’s service schedule, it was found feasible to start this test with a ‘quay trial’ outside Hamburg, Germany, on 1st-2nd October 2000. During this trial, all systems were tested with very satisfactory results – including perfect dead slow operation at 15 r/min.

The final step before the vessel resumed its schedule – now as an Intelligent Engine, i.e. without a camshaft – was a sea trial wich was carried out in the presence of surveyors from Det Norske Veritas in order to have the final approval from DNV and to maintain the vessel´s certificate.

This sea trial was carried out off Borneo on 7th and 8th November 2000. The final approval document from DNV states: ‘All tests were passed and it is judged that the engine and associated systems perform equally as good or better with the Intelligent Engine system in operation as with the traditional camshaft system’.

Thus, the end of the successful sea trial marked the beginning of the long-term service test which will be conducted over a period of some 10,000 operating hours to confirm the efficient and reliable operation of both the IE systems and the engine proper.

Fig. 21: Mode Selection Display

Fig. 22: Main Status Display

Commercialization of the IE Concept

In 1999, two V-Max class ULCCs  (Fig. 23) were ordered at Hyundai Heavy Industries in Korea for delivery in first-half of 2001, each with two 7S60ME-C engines, the ‘Intelligent Engine’ version of the well-established 7S60MC-C engine.

As a result of the previously mentioned delays in the development of the control software, and in order to ensure that the vessels are delivered on time, it has been agreed to make provision for conventional operation during the initial service period of the two vessels. The engines will be delivered prepared for later conversion to the 7S60ME-C version and will have the PMI on-line cylinder pressure measuring system, the CoCoS-EDS engine diagnosis systems, the CoCoS-MPS maintenance planning system and the electronic cylinder lubrication system in operation from the outset.

This will allow time to gain appropriate service experience with M/T Bow Cecil. Subsequently, the engines will be converted to proper 7S60ME-C ‘Intelligent’ engines during the scheduled docking of the vessels. At that time, the conventional camshaft system will be removed and replaced by the IEsystems, which will utilise the existing camshaft housing as oil pan and foundation.

Chapter-3

The First Commercial ME Engine

After a highly successful experience with the prototype 6L60MC/ME engine, Odfjell ASA, Norway, commissioned the World’s first dedicated ME engine, a 7S50ME-C, from MAN B&W Diesel’s Frederikshavn Works.

This particular engine will be installed in to a new building, KF 144. It is destined to power a chemical carrier being built by the Kleven Florø yard, Norway. MAN B&W Diesel are also supplying the GenSets and Controllable Pitch Propeller systems for the ship.

Unlike the prototype, this engine was designed and built without a camshaft –making it a truly cam-less engine. The functions of the camshaft have now been taken over by a fully integrated and computer controlled electro-hydraulic Engine Control System (ECS).

The ECS system controls the timing of the fuel injection through close monitoring of the crankshaft position via a tacho system, which is far more accurate and responsive than any mechanical method of control. This results in savings in fuel and lube oil consumption and at the same time gives greater manoeuvring control.

In addition to this highly efficient and controllable system, other MAN B&W Diesel innovations have also been integrated into this electronic engine. The Alpha Lubricator ACC has also been specified in addition to the CoCoS-EDS – the very successful engine monitoring and diagnostic system from MAN B&W Diesel.

The most visually different aspect of this engine, when compared to the older designs, is the removal of the timing chains. This change, in combination with the removal of the camshaft, has resulted in weight savings. In addition to this being a compact engine, hence the designation ME-C, the removal of the chains also gives the opportunity to further reduce the overall length of the engine.

Fig. 1: Completed – the first commercial ME engine

What is a cam-less engine

In this engine, the camshaft functions are replaced by an electronically controlled set of actuators. These actuators control the Starting air valves, Start and Reversing sequences, Governor function, Auxiliary blowers, Electronically Profiled Injection (EPIC) and Exhaust valve actuation.

This is done with far greater precision than camshaft-controlled engines. The exhaust valves, as on the MCengines, are opened hydraulically and closed by an ‘air spring’. The actuator is hydraulically driven by pressurized control oil via an on/off type valve.

The Starting air distributor has now been replaced by electronically controlled on/off valve which, in conjunction with the ECU and the CCU, control the Starting air valves.

The hydraulic power is provided by the Hydraulic Power Supply units placed at the aft end of the engine. The cam-less system, being electronically controlled, is fully integrated with other MAN B&W Diesel developments such as more efficient fuel and lube oil injection and the CoCoS engine diagnostic platform. This control makes the overall optimisation of each system even more effective and reliable.

The ECS can fully control and optimize the combustion process at any load by electronically controlling the valves according to the crankshaft position.

Electronic Control

The engine is controlled and monitored via the ECS. This platform encompasses several integrated units: the Engine Interface Control Units (EICU), Engine Control Units (ECU), Auxiliary Control Units (ACU) and Cylinder Control Units (CCU).

Fig. 3: Cross section – the first commercial ME engine

The EICUs handle the interface to external systems.

• The ECUs perform engine control functions: engine speed, running modes and start sequence.

• The ACUs control the hydraulic power supply and auxiliary blower pumps.

• The CCUs control fuel injection, valve actuators and starting air valves.

Reductions in the Specific Fuel Oil Consumption (SFOC) are achieved at part load. This is due to the maximum pressure being maintained over a wider load range and without overloading the engine.

Fig. 2: Hydraulic power supply filtration unit

Alpha Lubricator ACC

Alpha ACC allows the cylinder oil dosage (g/bhph) to be controlled in such a way that it is proportional to the amount of sulphur (g/bhph) entering the cylinder with the fuel.

This is achieved by making the cylinder oil dosage proportional to the sulphur percentage in the fuel and to the engine load (fuel amount).

The main element of the cylinder liner wear is of a corrosive nature, and the amount of neutralising alkalinic components needed in the cylinder will therefore be proportional to the amount of sulphur (which generates sulphurous acids) entering the cylinders.

A minimum cylinder oil dosage is set in order to satisfy other requirements of a lubricant, such as providing an adequate oil film and detergency properties.

Fig. 4: Top of engine

Fig. 5: Tacho system and hydraulic power supply system

Computer Controlled Surveillance System (CoCoS)

The CoCoS system has been specified as the engine monitoring, diagnostic and maintenance overview system on this engine. It is a comprehensive collection of MAN B&W Diesel-developed software, which is designed to detect various data, determined through the alarm system as well as other sensors in order to keep the engine working in its optimum state.

The CoCoS system’s four major programme groups consist of: the Engine Diagnostic System (EDS), a Maintenance Planning System (MPS), a Stock Handling and Spare Parts Ordering (SPO) facility and the Spare Parts Catalogue (SPC).

The EDS continually monitors all stored operating parameters for the entire lifetime of the engine, and provides a warning to the attendant staff if it suspects a problem is developing. If a problem is likely to occur, the appropriate work can be scheduled through the MPS, perhaps to coincide with other planned maintenance work. The MPS normally shows scheduled maintenance work together with timing instructions, list of required tools, spare parts and manpower requirements.

While scheduling maintenance, the SPO system automatically checks whether the spare parts are available (while allowing for a minimum and safety reserve), and the SPC gives the opportunity for the staff to display them (either in graphical or textual form).

The aim of the system is to prevent longer than necessary off-service repair time by increasing the engine’s availability and reliability, thus reducing operational costs. Additional savings can also be achieved through the appropriate scheduling of maintenance and spare parts ordering.

PMI System

The PMI system is a computerised tool for evaluation cylinder pressures in MAN B&W Diesel engines. It consists of a hand held transducer and control unit, which interfaces with a PC.

A single operator can collect and display a complete set of measurements in less than fifteen minutes. It uses a high performance piezo-electric pressure transducer and an advanced crankshaft angle trigger system for determining the TDC of each cylinder to reliably and precisely measure cylinder pressures.

The cylinder pressure data is presented as easy-to-interpret measurement curves on the PC as well as in tabular form. By calculating the max. pressure deviation of each cylinder and computing index settings for balanced output from all cylinders, the engine output can be adjusted for enhanced performance.

The system automatically calculates effective power, mean indicated pressure pi , and gives proposals for fuel pump index adjustments.

Alphatronic 2000 Control System

This electronic propulsion control system for ships with CP propellers enables the navigator to manoeuvre the ship from the bridge. This can be done without consideration for engine load conditions as the system automatically enacts an overload protection. The propulsion control can be transferred at any time to other control areas such as the bridge wing or control room panel. A separate emergency back-up system, as required by the major classification societies, maintains a pre-set engine speed and propeller pitch, and is physically integrated into the control panel.

ME  ENGINE ADVANTAGES

                        Variable electronically-controlled timing of fuel injection and exhaust valves for lower specific fuel consumption and better performance parameters

·         Lower rpm possible for manoeuvring

·         Better astern and crash stop performance

·         Improved emissions characteristics, such as lower NOx and smoke values at any load

·         Equalized thermal load in and between cylinders minimizing the risk of premature need for overhaul

·         System incorporating performance monitoring to promote longer times between overhauls.

CHAPTER-4

SERVICE EXPERIENCE 2008, MAN B&W ENGINES ME/ME-C AND MC/MC-C ENGINE SERIES

The number of electronically controlled engines in service continues to grow  and, at the time of writing, more than 500 engines are on order or in service.

At the end of 2007, the first S40ME-B engine was prototype-tested at STX in Korea, Fig. 8.1. These tests mark the beginning of an era where the full potential of the electronic  fuel injection  with “rate shaping” (or “injection profiling”)  is utilised on production  engines giving a very attractive NOx/SFOC relationship.

Fig. 8.1: 6S40ME-B engine

At the beginning of January 2008, the first four LNG carriers with 2 x 6S70ME-C engines (Fig. 8.2) were in service. During 2008, this number will increase to 20 vessels.In addition to the service experience  update for the ME/ME-C engine series, this paper will describe the recent service  experience relating to conventional mechanical issues of MAN B&W twostroke engines. The condition-based overhaul (CBO) concept and an update on monitoring systems will also be given.

Fig. 8.2: LNG carrier with 2 x 6S70ME-C engines

Update on Service Experience, ME/ME-C Engine Series

At the end of 2007, 1 0 ME/ME-C engines were in service. The reporting will be divided into the various sub-systems  of the ME/ME-C engines. These are the  hydraulic cylinder unit (HCU), the multi  purpose controller (MPC), the hydraulic  power supply (HPS) and the servo oil system.

Hydraulic cylinder unit (HCU)

For the HCU, we will concentrate on two main topics, i.e. the ME control valves and the exhaust valve actuator system.

ME control valves

ELVA/ELFI valves(Curtiss Wright supply) ELVA/ELFI configuration (one control

valve for exhaust valve actuation and another control valve for fuel injection control) are in service on 20 plants. For the on/off ELVA valve, a modified high-response valve is undergoing service testing. When this service testing is concluded, the 20 plants will be  updated and service issues with the ELVA/ELFI configuration will then be solved.

FIVA Valve (Curtiss Wright version) The feedback loop of the FIVA valve position control, Fig. 8. , has caused  untimed injection and untimed exhaust valve operation owing to various reasons.  These reasons are related to the FIVA valve itself in some cases, and in  other cases to the part of the feedback loop in the multi purpose controller  (MPC), see multi purpose controller chapter.

In the original version, the electronics on the printed circuit board (PCB) in the Curtiss Wright FIVA valve showed thermal instability causing untimed actuation of the valve. The reason was an analogue voltage regulator generating

Fig. 8.3: FIVA valve position control

an excessive amount of heat raising the temperature by 5ºC on the PCB. In some cases, this caused a temperature  shutdown of the LVDT converter in the feedback loop, resulting in the abovedescribed  unstable function of the FIVA valve. The solution was to exchange  the analogue voltage regulator with a switch mode regulator, Fig. 8.4. Hereby,  the temperature of the PCB was lowered by approx. 5ºC.

Fig. 8.4: FIVA valve feedback failure: exchange of analogue voltage regulator with switch mode voltage regulator

Furthermore, in order to safeguard against untimed movement of the FIVA main slide due to an erroneous feedback signal, improved supervision is introduced by new software, see multi purpose controller chapter. In 2007, we experienced a cylinder cover

lift twice on testbed with 6S70ME-C engines. The reason for these incidents was untimed movement of the FIVA valve main slide owing to a drilling chip left inside the main slide during production, Fig. 8.5. After discovering this production mistake, we have, together with the sub-suppliers, cleaned/re-machined approx. 500 main slides to avoid loose drilling chips inside the FIVA valves.

Fig. 8.5: CWAT FIVA valve: chips found in main slide

Fig. 8.6: CWAT FIVA valve: Movement of pilot valve and main slide

Fig. 8.6 gives an explanation of what happens if a loose drilling chip is stuck between

the pilot slide and the main slide.

Fig. 8.6 (left hand side) shows the valve in balance. This means that the constant pressure on the bottom of the main slide is balanced by a pressure creating a similar force in downward direction, thus keeping the slide in neutral (“zero”) position.In order to open the exhaust valve or to stop fuel injection (Fig. 8.6, centre), the pilot slide should be moved downward, thereby increasing the pressure on the top of the main slide and moving the main slide downward. This will result in exhaust valve opening or stop of fuel  injection.

When the pilot slide is moved upward(Fig. 8.6, right hand side), pressure on the top of the main slide is decreasing and the main slide is moved upward enabling closure of the exhaust valve  or fuel injection. If a drilling chip is stuck in between the pilot and the main slide  when the exhaust valve is closing, there is a risk of fuel injection just after closing  of the exhaust valve. This will create an excessive pressure build-up in the combustion chamber and a risk of  cylinder cover lifting. This was the cause of the two cylinder cover lifts on the  6S70ME-C engines on testbed in 2007.

FIVA Valve (MAN B&W version) During 2007, the first vessels with MAN B&W FIVA valves controlling ME engines went into service.

The MAN B&W FIVA valve can be seen in Fig. 8.7. It consists of a valve main

body on which the Parker pilot valve and the H. F. Jensen feedback sensor are mounted. For the Parker valve, we have seen a number of units failing because

of:

Fig. 8.8a: Broken bushing, b: Damaged wire strip, c: Parker valve

A: Broken bushing for the pilot slide,Fig. 8.8a. This item was rectified during the                                                                                                                                  prototype testing period

B: Earthing failure owing to damage ofa flexible wire strip inside the valve, Fig. 8.8b

C: Malfunction owing to failing operational amplifier, Fig. 8.8c

Fig. 8.9a: Redesign of rod for sensor in H.F. Jensen feedback sensor

A: Breakage of the rod in the sensor. The rod in the sensor has been redesigned, Fig. 8.9a

B: Broken or loose connection between the print board and the external connector (type: Canon),Fig. 8.9b. Redesign of the connection has solved the problem. In parallel with solving teething problems with the Parker pilot valve and the H. F.  Jensen feedback sensor, other  makes of pilot valves and feedback sensors are being tested. Parker valves with certain serial numbers  have been replaced in service.

Fig. 8.9b: Connector breakdown, H.F.Jensen feedback senso

With respect to the H. F. Jensen feedback sensors, we have experienced two different problems:

FIVA Valve (Bosch Rexroth version) Service tests of the Bosch Rexroth FIVA valve, Fig. 8.10, on a 12K98ME  have been concluded successfully. Bosch Rexroth FIVA valves are now the  third alternative for control valves for the present ME engine series.

Fig. 8.10: Bosch Rexroth FIVA

Cavitation in the exhaust valve actuation system

Cavitation in the exhaust valve actuation system has been seen in the exhaust valve top part, Fig. 8.11a, as well as in the exhaust actuator top cover, Fig. 8.11b. Furthermore, damage to the oil inlet non-return valves on the actuator top cover indicates excessive pressure fluctuations in the exhaust valve actuation system. An orifice in the drain line from the FIVA valve, Fig. 8.12, has been introduced to reduce the acceleration of the actuator piston and hereby eliminating cavitation on the actuation side At the time of writing, we are monitoring cavitation development after the introduction of the orifice in the FIVA return line. However, in parallel, we are testing further modifications:

A: Reduced braking of the exhaust valve by introduction of an orifice (small hole) in the damper piston, Fig. 8.1 .

B: Low-pressure oil supply in the top of the exhaust valve, Fig. 8.1 . It is considered to move one of the lowpressure supplies on the actuator, Fig. 8.14, to the top of the exhaust valve.

Fig. 8.11a: Cavitation in exhaust valve top part      Fig. 8.11b: Cavitation in exhaust actuator                    top cover

Introduction of ring orifice corresponding to a 20 mm orifice in the hydraulic system for exhaust valve on K98ME-C

Fig. 8.12: Orifice in the drain line from the FIVA valve

Fig. 8.13: Exhaust actuation system, scheduled test rig tests

Fig. 8.14: Non-return valves in low pressure supply lines

Multi purpose controller (MPC)

In 2007, we experienced one severe case of cylinder cover lift on a 6S60ME-C engine in service. After investigations into the parts involved on the cylinder unit in question, it was concluded that  the reason was an error in the feedback loop for the FIVA control, Fig. 8. . However, in this case the error was in the MPC part of the feedback loop. A loose/broken connection in the feedback circuit of the MPC was found during the investigation, see Fig. 8.15. Countermeasures in this relation were divided into three parts.

Fig. 8.15: Broken/loose connection in the MPC

Firstly, a circular letter warning against a specific alarm sequence was issued in order to exchange MPCs with similar potential defects. This circular letter was sent to all operators of ME engines.

Secondly, it was concluded from tests that the reason why the error in the feedback loop of the MPC caused an untimed injection was that the feedback signal froze on a low value. When the closed loop control tried to rectify the position of the main slide in the FIVA valve, it moved the main slide towards fuel injection and continued to do so until injection (untimed) was accomplished. This was done because of the frozen low-value feedback signal.

Based on this knowledge, it was decided to invert the feedback signal, Fig. 8.16. By doing this, a frozen low value feedback signal will result in a FIVA main slide movement towards untimed opening of the exhaust valve. This is considered to be “failing into safe

mode”.

Fig. 8.16: FIVA valve flow area diagram

Thirdly, in order to safeguard further against similar incidents, a new software version with closer supervision of the feedback signal [1] and additional supervision of the fuel plunger movement [2] has been introduced, Fig. 8.17. Control processes including the supervisions [1] and [2] are seen in Fig. 8.18.

All ME engines in service have been or will be updated with the above ountermeasures.

Fig. 8.17: FIVA valve position control

Fig. 8.18: Crankshaft related control processes

Hydraulic power supply (HPS)

In 2006, we experienced a breakdown of the bearings in an HPS on a 12K98ME engine. A design review was initiated and modifications were implemented, both for new engines and for engines in service. After this incident we have not seen further incidents

relating to the HPS bearing/bushing design on the ME engines.

For a series of the first S70ME-C plants, the chain wheel and gear wheel assembly on the HPS common shaft has shown to be under-dimensioned, Fig. 8.19. An upgrade of the bolt connections has been introduced on the concerned vessels in service.

Servo oil system

For the present ME engines, two alternative servo oil systems are available:

A: A standard system where engine system oil is processed through a 6-10 µm full-flow fine filter and then led into the hydraulic pumps of the HPS.

B: An optional system where a separate servo oil system with a separate tank system is used, Fig. 8.20. The oil is cleaned by a cleaning unit (filter or purifier) mounted on the separate oil tank.

During 2007, we experienced one case of severe contamination of the servo oil system owing to a breakdown of the ship side transfer pumps. This happened on an installation equipped with a separate servo oil system (B).

Fig. 8.19: S70ME-C assembly of shaft for hydraulic pump

Fig. 8.20: Separate hydraulic oil system, initial version

Apparently, the screw type pumps produced the contaminating products rather quickly and, therefore, a lot of debris ended up inside the ME control valves, see Fig. 8.21.

After this incident, we have revised our specification for the separate servo oil system, Fig. 8.22. The important change is that a 6 µm full-flow fine filter has been introduced, also on the separate servo oil system.

For engines in service with a separate servo oil system, we recommend to add a ‘‘water-in-the-oil monitor’’, connect  the oil temperature measurement to the alarm system and install a metal detector just before the hydraulic power supply.

Fig. 8.22: Separate hydraulic oil system, updated version

Update on Service Experience, MC/MC-C Engine Series

In the following, we will describe the recent service experience on the MC/ MC-C engine series, with focus on condition based overhaul (CBO) and update on monitoring systems. CBO is of couse also relevant and possible for ME/ME-C engines.

Condition based overhaul (CBO) of pistons

The experience with our engines with the latest updated combustion chamber design, i.e. with Oros shape and  the latest piston ring design, slide fuel valves and optimised temperature levels, counts more than seven years of operation. Against this background, we have gained valuable knowledge about

the need for piston overhauls compared with earlier experience.

The “Guiding Overhaul Interval” for pistons, previously set to 12-16,000 hours, appears to have been set too conservatively. Normally, the need for piston overhaul does not arise until much later, and extensions up to 2,000 hours are possible. However, the fact is that the scatter is large, and many factors are

This calls for a CBO strategy, the objective being to obtain the highest number possible of safe running hours. Preferably, overhauling should only be carried out when necessary.

The most important factor in a CBO strategy is the evaluation of the actual condition, by means of regular scavenge port inspections and logging of wear and hot corrosion. All the decisive factors for piston  overhaul can be checked via inspections through the scavenge air ports.

The most important factors for piston overhauls are fig 8.23:

• Piston ring wear

• Max. amount of hot corrosion of piston top allowed on the centre part (where it is normally highest)is 9/12/15 mm on, respectively, 80/90/98-bore engines

• Ring groove clearance Max. recommended clearance is 1.0 mm on the 80 and 90-bore engines,and 1.1 mm on 98-bore engines

• Sticking, broken or collapsed piston rings or leaking pistons

• Macro-seizures on piston ring running surfaces.

            Fig. 8.23: K98 example. The four (4) important factors for piston overhaul

Inspection and logging of the actual cylinder condition and wear should be performed regularly to become familiar with the wear-and-tear development in the cylinder. At the beginning, intervals should be short, e.g. every second to third week. The intervals can be prolonged as confidence builds up.

The following factors should be measured and recorded:

•Top piston ring wear, defined by measuring the remaining depth of the CL grooves.

•Ring groove clearances, measured with a feeler gauge.

•Estimated piston burnings on large bore engines, measured by means of a template via the scavenge ports.

Our standard sheets “Cylinder Condition Report” and “Inspection through Scavenge Ports” can be used, forming the ideal documentation for later review and for making trend curves for future wear forecasts, Fig. 8.24.

Fig. 8.24: 10K98MC-C, unit no. 7, at 23,500 hours without overhaul. The condition does not call for piston overhaul

The running surfaces of the piston rings are the best indicators of the cylinder condition in general. If the ring surfaces appear to be in good condition and free from scratches, micro or macroseizures, the liner will also be in good condition, Figs. 8.25-8. 0.

Figs. 8.25-8.27 describe conditions of the new cermet coated ring packages with alu-coat running-in. Figs. 8.28-8. 0 describe the conditions of the alu-coated ring packages.

Conversely, if the liner appears damaged by active seizures (if the wave-cut  pattern has disappeared on the lower  cylinder part visible through the ports), the rings will also be affected, and most likely the unit has to be overhauled.

As mentioned above, the wear on the top piston rings can be determined by measuring the remaining depth of the  CL grooves using a Vernier gauge, but the wear can also be estimated visually  simply by checking the size of the remaining rounding on the upper and lower edges of the running surfaces.

            From new, the rounding has a radius of 2 mm on 80/90/98-bore engines.

Thus, a simple visual inspection  through the scavenge ports confirming that the rounding is still visible or partly  visible is an indication that the wear limit has not been reached, and that many more hours are left before piston  overhaul is necessary. For further information, we refer to our Service Letter SL07-48 .

ce Experience ME/M

E Fig. 8.31: W-seat and DuraSpindle combination CBO of exhaust valves

Fig. 8.32: W-seat in combination with nimonic spindle and DuraSpindle

For the exhaust valve, the use of Wseat, Fig. 8. 31, and either nimonic valve spindle or DuraSpindle has improved  the overhaul intervals to longer than  2,000 hours. Fig. 8. 32 shows examples of an excellent condition without  overhaul with combinations of a W-seat/ nimonic spindle and a W-seat/DuraSpindle

achieved on an S60MC engine  after 25,500 hours and ,900 hours, respectively.

Fig. 8.33: Controlled oil level (COL) design

Clean lubricated spindle guide and a sealing ring with a wear profile which well indicate running up to 30,000- 35,000 hours.

7K98MC: COL test unit, inspection after running hours 20,468 hours

Fig. 8.34: Inspection of COL design

For exhaust valve stem seal, the socalled  controlled oil Level (COL) design, Fig. 8.33. , indicates that also tem seal overhaul intervals can be extended to 30,000- 5,000 hours, based on results from several test units on 98, 90 and 60  bore engines. This illustrated by Fig. 8. 34 showing an open-up inspection on a K98.

CBO of bearings

Since the late 1990s, a positive development with respect to main bearing damage has been seen.  Despite the  heavy increase in the number of main bearings on MC/MC-C engines, Fig. 8. 35, the reported damage frequency remains very low, see Fig. 8.36.

Fig. 8.35: Main bearing population 1982-2008 divided into bearing types

For other bearing types (crosshead and crankpin bearings), the damage frequency is also very low.

Fig. 8.36: Thick shell main bearing damage statistic

However, in a few cases we experienced  severe damage causing long-term offhire periods involving also costly repairs  of the bedplate and/or the crankshaft.  An example is shown in Fig. 8. 37. In this case, the reason for the damage was  incorrect assembly after an open-up inspection of a main bearing after sea trial.

Fig. 8.37: Main bearing damage on 6S70MC-C . 6S70MC-C on maiden voyage.*Continued running for 1½ hrs after 1st alarm,  Main bearing incorrectly assembled after inspection,3½ month repair

This sequence of events following  open-up inspections of bearings is unfortunately being reported from time  to time. We have therefore changed our instruction material, not calling for  open-up inspection at regular intervals. In parallel, we have made so-called bearing wear monitoring (BWM) systems  a standard on engines ordered in  2008. BWM systems can also be retro- fitted on existing engines

In principle, the BWM system monitors  all the major bearings (main, crankpin and crosshead) by measuring the distance to the bottom dead centre of the crosshead, Fig. 8.38. The distance will decrease if wear occurs in one of the major bearings, and the BWM system can then give an alarm.

Fig. 8.38: Bearing Wear Monitoring (BWM), position of sensors

By monitoring wear in the major bearings, condition based monitoring (CBO)  of bearings is introduced, and regular  open-up inspections can be limited to  fewer than previously. Optimally, openup  inspections should, if at all needed,  only be carried out during dry-dockings  or when indications (bearing metal in

bedplate or BWM alarm) call for it.

This revised strategy will further limit  the cases of severe bearing breakdowns.

Also water in oil (WIO) monitoring systems have been added to the standard instrumentation for newly ordered engines. This is especially important

in relation to crosshead bearings with lead overlayer being sensitive towards  corrosion due to a too high  water content  in the system oil. For engines in  service, WIO is described in service letter SL05-460.

Time between overhaul (TBO) for turbochargers

For turbochargers, the major makers  are now promoting extended times between major overhauls

(Fig. 8. 39).This means that for new turbochargers, it will be realistic to require major overhauls only during docking of the vessel. The overhaul intervals will then in many  cases be five years.

Fig. 8.39: Modern turbocharger enabling more than 30,000 hours between major overhauls

CHAPTER-5

THE SULZER RT-FLEX COMMON-RAIL SYSTEM DESCRIBED

Rather than ‘electronically controlled’, it would be more accurate to describe Sulzer RT-flex engines as being computer controlled. Th is is because in the RT-fl ex system, engine functions are fully programmable, perhaps  limited only by the designers’ imagination and the laws of nature. Th e challenge is to use this freedom to create  practical benefi ts for engine users.

The common-rail concept was adopted also because it has the advantage that the functions of pumping and injection control are separated. Th is allows a straightforward approach to the mechanical and hydraulic aspects of the design, with a steady generation of fuel oil supply at the desired pressure ready for  injection. Th e common-rail concept also has the unique advantage that it allows the fuel injection valves to be  individually controlled. Usually there are three fuel injection valves in each cylinder cover, and in the Sulzer  RT-fl ex engines they are operated mostly in unison but nder certain circumstances they are operated separately  for optimum combustion performance.

The common-rail concept thus provides an ideal basis for the application of a fully-integrated electronic control. Th e combined fl exibilities of common rail and  electronic control provide improved low-speed operation, engine acceleration, balance between cylinders, load  control, and longer times between overhauls. They also ensure better combustion at all operating speeds and loads, giving benefi ts in lower fuel consumption, lower  exhaust emissions in terms of both smokeless operation at all operating speeds and less NOX emissions, and also a  cleaner engine internally with less deposits of combustion residues. Engine diagnostics are built into the system,  improving engine monitoring, reliability and availability. As the common-rail system is built specifi cally for reliable

Fig. 1: Principal elements of the common-rail system on a Sulzer RT-fl ex engine. Note that there are variations on this arrangement in the various RT-fl ex engine types depending upon the engine type and number of cylinders.

operation on heavy fuel oil, it detracts nothing from the well-established economy of low-speed marine diesel engines but rather  opens up new possibilities for even better economy, ease of operation, reliability, times between overhauls and lower exhaust emissions.

It is more than ten years since development of the Sulzer RT-fl ex common-rail system began and more than 20 years since the first tests were made with electronically-controlled fuel injection in Winterthur, Switzerland.

The early camshaftless systems developed for Sulzer engines relied on integral electronic control but used  individual, hydraulically-operated fuel injection pumps. However the change in injection concept from the individual, hydraulically-operated fuel injection pumps  to a common-rail system in 1993 was made because the system with individual pumps did not offer potential  for further technological development despite it having integral electronic control. Electronic control was found to be insufficient by itself and a new fuel injection concept was recognized  as essential. Common rail was seen as the road ahead and it is applied in Sulzer RT-fl ex engines.

Sulzer RT-flex engines are thus notably different from other electronically-controlled low-speed diesel engines today as Sulzer RT-flex engines are unique in combining the benefits of both common-rail systems and electronic control.

Sulzer RT-fl ex system

Sulzer RT-fl ex engines are essentially standard Sulzer  RTA low-speed two-stroke marine diesel engines except that, instead of the usual camshaft and its gear drive, fuel injection pumps, exhaust valve actuator pumps, reversing servomotors, and all their related mechanical control gear, they are equipped with a common-rail system for fuel injection and exhaust valve actuation, and full electronic control of engine functions. There are four principal elements in the Sulzer RT-flex common-rail system: the rail unit along the side of thecylinders, the supply unit on the side of the engine, a filterunit for the servo oil, and the integrated electronic control system, including the crank angle sensor.

The RT-fl ex engines are thus equipped with common rail systems for:

• heated fuel oil at pressures up to 1000 bar,

• servo oil at pressures up to 200 bar,

• control oil at a constant pressure of 200 bar,

• engine starting air system.

RT-fl ex Sizes

The hardware in the RT-fl ex system is being developed in four principal sizes for the six engine types currently  in the programme  (see Table 1). The six RT-fl ex engine types cover a power range of 8100 to 80,080 kW (11,000 to 108,920bhp).

This illustrates one of the advantages of the commonrail system in that hardware is standardized for groups of engine types, not just for the various cylinder numbers.

Fig. 2: Schematic of the common-railsystems in Sulzer RT-fl ex engines

Supply unit

Fuel and servo oil are supplied to the common-rail system from the supply unit which is driven through gearing  from the engine crankshaft.

In the first few RT-fl ex engines, the supply unit is on the exhaust side of the engine so that it could be lower  down without interfering with access to the crankcase. However, for all subsequent engines, the location of the  supply unit has since been standardized  on the front of  the engine (on the same side as the rail unit) and at about mid height. This keeps the engine ‘footprint’ small so  that the engines can be located far aft in ships with fine after bodies.

The supply unit is naturally at the location of the gear drive: at the driving end for five- to seven-cylinder engines, and at the mid gear drive for greater cylinder numbers.

Fig. 3: Supply unit for a Sulzer 12RT-fl ex96C engine with the fuel pumps in a Vee-form

arrangement on the left and servo oil pumps on the right-hand face of the central gear drive. The fuel pumps all deliver into the collector seen above the fuel pumps.

The supply unit has a rigid housing of GGG-grade nodular cast iron. The fuel supply pumps are arranged  on one side of the drive gear and the hydraulic servo-oil pumps are on the other side. Th is pump arrangement allows a very short, compact supply unit with reasonable

Fig. 4 above: Supply unit on a Sulzer 12RT-fl ex96C engine with the fuel pumps in a Vee-form arrangement on the left and servo oil pumps on the right-hand face of the

central gear drive.

Fig. 5 right: Cutaway drawing of the fuel supply pump element for RT-fl ex96C engines.

service access. The numbers, size and arrangement of pumps are adapted to the engine type and the number of engine cylinders.

For RT-fl ex Sizes I and IV, the supply unit is equipped with between four and eight fuel supply pumps arranged in Vee-form. The Size 0 supply unit, however, has just two or three supply pumps in-line.

Two sizes of fuel pumps are employed for all RT-fl ex engines, both based on the well-proven injection pumps used in Sulzer Z-type medium-speed four-stroke engines though with some adaptations to suit their function as supply pumps and to raise their volumetric                efficiency up to a very high degree. For Sizes 0 and I, the fuel pump elements are based on the injection pumps of Sulzer ZA40S engines, while the Size IV pumps are based on the injection pumps of the Sulzer ZA50S engine type.

The fuel supply pumps are driven through a camshaft with three-lobe cams. This camshaft cannot be compared with the traditional engine camshaft. It is very short and

of much smaller diameter, and is quite differently  loaded.

There is no sudden, jerk action as in fuel injection pumps but rather the pump plungers have a steady reciprocating motion. With tri-lobe cams and the speed-increasing gear drive, each fuel supply pump makes several strokes during each crankshaft revolution. The result is a compact supply unit.

Two designs of camshaft are employed. For Size I it is manufactured in one piece. For Size IV, the camshaft is assembled from a straight shaft on to which the tri-lobe cams are hydraulically press fi tted. This latter form of 

Fig. 6: Close view of the fuel supply pumps in fi gure 4showing the regulating linkage.

Fig. 7: Various RT-fl ex equipment on the half-platform of a 12RT-fl ex96C engine. From left to right, these include (A) the local engine control panel, (B) the automatic fi ne fi lter for servo and control oil, (C) the two electrically-driven control oil pumps and (D) the supply unit.

construction has been used for decades in Sulzer Z-type engines. It is extremely service friendly and minimizes maintenance cost. Th e camshaft bearings have an aluminium running layer.

The fuel delivery volume and rail pressure are regulated according to engine requirements through suction control with helix-controlled fi lling volume regulation of the fuel supply pumps. Suction control was  selected for its low power consumption as no excess fuel is pressurised.

The roller guide pistons contain the floating-bush bearings for the rollers as they are used on all Sulzer  RTA- and Z-type engines. Owing to the moderate accelerations given by the tri-lobe cam shape, the specific loads of roller bearings and pins as well as the Hertzian  pressure between cam and roller are less than for the original pumps in ZA40S and ZA50S engines.

For every individual fuel pump element of the supply  unit, the roller can be lifted off the cam, blocked and manually taken out of service in case of difficulties. The fuel pumps deliver the pressurized  fuel to an adjacent collector from which two independent, doublewalled  delivery pipes lead upwards to the fuel rail. Each delivery pipe is dimensioned for full fuel flow.

The collector is equipped with a safety relief valve set to 1250 bar. An equivalent arrangement of a collector and  duplicated independent, double-walled delivery pipes is

employed for the servo oil supply.

Servo oil

Servo oil is used for exhaust valve actuation and control. It is supplied by a number of swashplate-type axialpiston hydraulic pumps mounted on the supply unit.

The pumps are of standard proprietary design and are driven at a suitable speed through a step-up gear. The working pressure is controllable to allow the pump power consumption to be reduced. The nominal operating pressure is up to 200 bar. The number and size of servo oil pumps on the supply unit depend on the engine output or number of engine cylinders. There are between three and six servo oil pumps.

The oil used in both the servo and control oil systems is standard engine system lubricating oil, and is simply taken from the delivery to the engine lubrication system. The oil is drawn through a six-micron automatic selfcleaning  fine filter to minimise wear in the servo oil pumps and to prolong component life.

After the fine filter, the oil flow is divided, one branch to the servo oil pumps and the other to the control oil pumps.

Control oil

Control oil is supplied at a constant 200 bar pressure at all engine speeds by two electrically-driven oil pumps,  one active and the other on standby. Each pump has its own pressure-regulating valve and safety valve attached.

The control oil system involves only a small flow quantity of the fine filtered oil. The control oil serves asthe working medium for all rail valves of the injection control units (ICU). The working pressure of the control oil is maintained constant to ensure precise timing in the  ICU. It is also used to prime the servo oil rail at standstill  thereby enabling a rapid starting of the engine.

Fig. 8 above: Cylinder tops and rail unit of a Sulzer 8RT-fl ex96C engine.

The electronic control units are  mounted on the front below the rail unit.

Fig. 9 left: Three-dimensional drawing of the inside of a rail unit for an RT-fl ex96C engine, showing the fuel  rail (A), the control oil rail (B) and the servo oil rail (C) with the control units for injection (D) and exhaust  valve actuation (E) on top of their respective rails. Other  manifold pipes are provided for oil return, fuel leakage return, and the   system oil supply for the exhaust valve  drives.

Fig. 10 below: Th e two sections of rail unit for a 12-cylinder RT-fl ex96C engine during the course of assembly.

Fig. 11: Cylinder tops of a 12-cylinder RT-fl ex96C engine with the rail unit under the platform on the left. Th e hydraulic pipesfor the exhaust valve drives arch up from the exhaust valve actuators on the servo oil rail, and the sets of triple high-pressure fuel injection pipes rise up from the injection control units on the fuel rail.

Rail unit

The rail unit is located at the engine’s top platform level, just below cylinder cover level. It extends over the  length of the engine. It is fully enclosed but has good  maintenance access from above and from the front. The  rail unit contains the rail pipes and associated equipment  for the fuel, servo oil and control oil systems. The starting air system is not included in the rail unit. For engines with up to eight cylinders, the rail unities assembled as a single unit. With greater numbers of  cylinders, the engines have a mid gear drive and the rail  unit is in two sections according to the position of the mid gear drive in the engine.

The fuel common rail provides storage volume for the  fuel oil, and has provision for damping pressure waves.   There is no need for energy storage under gas pressure. The volume of the common-rail system and the supply  rate from the fuel supply pumps are such that the rail pressure is very stable with negligible pressure drop after each injection.

In the RT-fl ex Size I, the high-pressure pipe for the fuel rail is modular with sections for each cylinder and flanged to the individual injection control units for each cylinder.

With the Size IV, the high-pressure fuel rail was  changed to a single-piece rail pipe to shorten assembly  time and to simplify manufacture. A single length of rail pipe is installed in each section of the rail unit. The only  high-pressure pipe flanges on the Size IV pipe are the end covers.

The common rail system is designed with very high safety margins against material fatigue. The fuel rail  pipe for instance has a very special inner shape to keep the stress amplitude in cross-bored drillings remarkably  low. The fact that, by definition, common rails have  almost constant pressure levels further increases the  safety against high cycle fatigue cracking compared to  conventional injection and actuator systems with high pressure cycles.

The high-pressure rail is trace heated from the ship’s heating system, using either steam or thermal oil.  The simplification of the fuel rail for Size IV, without  intermediate flanges, compared with that for Size I allowed the trace heating piping also to be simplified. The trace heating piping and the insulation are both slimmer,  allowing easier service access inside the rail unit.

Fig. 12: Inside a Size IV rail unit  during assembly. The exhaust valve actuator (A) is mounted on  the servo oil rail and the injection control unit (B) is on the fuel rail. Next to the fuel rail is the smaller  control oil rail (C) and the return pipe for servo and control oil (D).

Injection control unit (ICU)

Fuel is delivered from the common rail to the injection  valves through a separate ICU for each engine cylinder. The ICU regulates precisely the timing of fuel injection, accurately controls the volume of fuel injected, and sets the shape of the injection pattern. The ICU has an injection control valve and a Sulzer electro-hydraulic rail valve for each fuel injection valve. Th e rail valves  receive control signals for the beginning and end of  injection from the respective electronic unit of the WECS (Wärtsilä Engine Control System).

There are three fuel injection valves in each engine cylinder except for the RT-fl ex50 which has two. The fuel injection valves are the same as those already employed in RTA engines, and are hydraulically-operated in the usual way by the high-pressure fuel oil. Each fuel injection  valve in a cylinder cover is independently controlled by the ICU for the respective cylinder so that, although all the injection valves in an individual cylinder normally  act in unison, they can also be programmed to operate separately as necessary.

For Size I, the individual ICU are arranged between  the sections of rail pipe but for Size IV the individual ICU are mounted directly on the rail pipe. The ICU for Size IV was adapted from that in Size I with the same  function principles for integral injection volume flow but  to suit the greater flow volumes involved.

The common-rail system is purpose-built for operation on just the same grades of heavy fuel oil as are already standard for Sulzer RTA-series engines. For this reason, the RT-fl ex system incorporates certain design features not seen in other common-rail engines using middledistillate diesel oils. The key point is that, in the ICU, the heated heavy fuel oil is isolated from the precision rail valves.

The Sulzer rail valves are bi-stable solenoid valves with an extremely fast actuation time. To achieve the longest possible lifetime, the rail valves are not energised for more than 4ms. This time is sampled, monitored and limited by the WECS. The valves’ bi-stability allows their position and status to be reliably controlled.

Exhaust valve control

The exhaust valves are operated by a hydraulic ‘push rod’, being opened by hydraulic oil pressure and closed by an air spring, as in the Sulzer RTA engines with mechanical

camshafts. But for RT-fl ex engines the actuating energy now comes from the servo oil rail. There is one exhaust  valve actuator (also known as the partition device) for each cylinder.

In the exhaust valve actuator, fine-filtered servo oil acts on the underside of a free-moving actuator piston, with normal system oil above the actuator piston for valve actuation. The adjacent hydraulic control slide is precisely activated by a Sulzer rail valve and controls the flow of servo oil to the actuator piston so that the exhaust valve opens and closes at precisely the correct time with appropriate damping. The exhaust valve actuator employs  the same Sulzer rail valves as are used for the ICU.

The exhaust valve drive on top of the valve spindle is equipped with two analogue position sensors to provide a feedback on valve operation to the WECS.

The electronically-controlled actuating unit for each cylinder gives full flexibility for exhaust valve opening  and closing patterns. At the same time, the actuating unit provides a clear separation of the clean servo oil and the normal system oil. Thus the exhaust valve hydraulics can be serviced without disturbing the clean servo oil circuit.

Operating pressures and system energy

The normal operating pressure for the fuel rail ranges up to 1000 bar. It is lowered for the best compromise  between BSFC (brake specific fuel consumption) and NOX emissions according to the respective engine load and to keep the parasitic energy demand low. It was determined years ago in engine tests in Winterthur that, under steady load conditions, the influence of fuel injection pressure on specific fuel  consumption in low-speed engines diminishes with increasing injection pressure. Thus, higher fuel injection pressures than are presently used in large two- stroke low-speed engines have no real benefit. Should an increase become necessary in the future, for instance in combination with other measures to reduce NOX emissions, the RT-fl ex system is ideal to cope with it. The additional, parasitic system energy would be very  limited indeed, as the increase is about proportional to the pressure increase.

Exhaust valve actuation requires a high volume flow of oil. With an appropriately stepped hydraulic piston diameter on the valve spindle both proper valve movement and low parasitic power could be achieved at the same time. Additionally, the servo oil pressure of 200 bar nominal is variably adapted to the minimum requirement over engine load to ensure a proper function and minimal power demand.

Fig. 15: The exhaust valve drive on top of the exhaust valve  spindle with the hydraulic   cylinder and the air spring. The two position sensors (not visible in this view) measure the radial distance to the cone to determine the spindle’s vertical

Starting air system

The starting air system of RT-fl ex engines is very similar to that in Sulzer RTA engines, except that its control is incorporated into the WECS. The starting air system, however, is installed outside the rail unit to facilitate overhaul access.

Electronic control

All functions in the Sulzer RT-fl ex system are controlled and monitored through the Wärtsilä Engine Control System (WECS). This is a modular electronic system with separate microprocessor control units for each cylinder, and overall control and supervision by duplicated microprocessor control units. The latter provide the usual interface for the electronic governor and the shipboard  remote control and alarm systems. The microprocessor  control units, or electronic control units, are mounted directly on the engine, either on the front of the rail unit or adjacent to it..

An essential input signal for WECS is the engine  crank angle. This is measured very accurately by two  sensors driven from a stub shaft on the free end of the crankshaft. The two sensors are driven by toothed belts so that axial and radial movements of the crankshaft are not passed to the sensors. The sensors are able to give the absolute crank angle position immediately that electrical power is applied.

At present RT-fl ex engines are being equipped with the WECS-9500 control system. However, this will be superseded in 2005 by the WECS-9520 control system. The new system provides simpler communication with the ship automation system and easier wiring for the shipbuilder. Only one electronic module is used throughout the new system, and there are fewer  equipment boxes which are also of simple, standard design. The functionality of WECS-9520 is the same as that of the WECS-9500 system.

Fig. 16: Electronic control units  beneath the front of the rail unit of a Sulzer RT-fl ex96C engine.

Sulzer RTA and RT-fl ex engines have standardized interfaces (DENIS) for remote control and safety systems.  The remote control and safety systems are supplied to the ship by a variety of approved manufacturers and DENIS (Diesel Engine Interface Specification) defines the interface between the engine-mounted equipment and the shipboard remote control and safety system.

With RT-fl ex engines, the remote control sends engine manoeuvring commands to the WECS. The remote control processes speed signals from the engine order telegraph according to a defined engine load program and fuelling limitations, and generates a fuel reference signal for the WECS according to DENIS.

The safety system function in RT-fl ex engines is basically the same as in conventional RTA engines, except that it has additional inputs for WECS slowdown and WECS shutdown signals, and some outputs to the WECS system.

Reliability and redundancy

Reliability and safety has the utmost priority in the RT-fl ex system. Although particular attention is given to  the reliability of individual items of equipment in the RT-fl ex system, the common-rail concept allows for  increased reliability and safety through its inherent  redundancy.

High-pressure fuel and servo-oil delivery pipes, the electrically-driven control oil pumps, and essential parts of the electronic systems are duplicated for redundancy.

Fig. 17: Inside one of the electronic control units shown in figure 16.

The duplicated high-pressure delivery pipes have stop cocks at both ends to isolate any failed pipe. Each single pipe is adequate for the full delivery. All high pressure pipes are double-walled for safety.

With a more traditional injection arrangement of one  fuel high-pressure pump to each cylinder, a failure of one  pump leads to the loss of that cylinder and the imbalance in engine torque requires a drastic power cut. In contrast,  with the RT-fl ex system in  hich all high-pressure supply pumps are grouped together and deliver in common to all  cylinders, the loss of any pumps has much less effect.

Indeed with larger RT-fl ex engines having several fuel pumps and several servo oil pumps there can be adequate redundancy for the engine to deliver full power with at least one fuel pump and one servo oil pump out of action. Should further pumps be out of action, there would be only a proportional reduction in power.

Every injection nozzle is independently monitored and controlled by the WECS. In case of difficulties, such as a broken high pressure line or a malfunctioning injector, the affected injection valve can be cut out individually without losing the entire cylinder.

The injection control unit ICU hydraulically excludes the injection of an uncontrolled amount of fuel. During the entire working cycle of the metering cylinder, there is never a direct hydraulic connection between fuel rail and the injectors. The maximum injection quantity is limited to the content of the metering cylinder as the travel of the metering piston is monitored. If the travel of the metering  piston should be measured as out of range, the subsequent injections of that ICU will be suppressed and an engine slow-down activated.

The ICU also serves as a flow fuse: if the metering piston should travel to its physical limit, it cannot return hydraulically and no further injection would be possible until it is reset.

If the stroke measuring sensor fails, the WECS system switches the ICU to a pure time control and triggers the  signal based on the timing of the neighbouring cylinders. Two redundant crank angle sensors measure the  absolute crank angle position which is evaluated through  WECS. WECS is able to decide which sensor to follow in case of a discrepancy.

The WECS main controller and all essential communication interfaces such as CAN-bus cablings  are duplicated for redundancy. WECS monitors the momentary position of each rail valve for proper function of each cycle before starting the next.

Fig. 18: Typical injection pattern of Sulzer RT-fl ex engines with all injection nozzles acting in unison showing needle lift, fuel rail pressure, injection pressure and cylinder pressure when all injection nozzles are operating simultaneously. Note the sharp beginning and ending of injection, the lack  of a significant pressure drop in the common rail during injection, and the small rail pressure fluctuations.

Operation and maintenance

Sulzer RT-fl ex engines are designed to be user friendly, without requiring ships’ engineers to have any special additional skills. Indeed the knowledge for operating and maintenance of RT-fl ex engines can be given in the same form as Wärtsilä’s usual one-week courses for Sulzer RTA-series engines given to ships’ engineers and owners’ and operators’ shore staff . The training time usually given to the camshaft system, fuel pumps, valve actuating pumps and reversing servomotors is simply given instead to the RT-fl ex common-rail system.

It has been seen from shipboard operation of the  RT-fl ex engines that the ships’ engineers quickly become comfortable operating the engines.

Key features of the Sulzer RT-fl ex system

The key features of the Sulzer common-rail system can be summarised as:

• Precise volumetric control of fuel injection, with integrated flow-out security

• Variable injection rate shaping and variable  injection pressure

• Possibility for independent action and shutting off of individual fuel injection valves

• Ideally suited for heavy fuel oil

• Well-proven standard fuel injection valves

• Proven, high-effi ciency common-rail pumps

• Lower levels of vibration and internal forces and moments

• Steady operation at very low running speeds with precise speed regulation

• Smokeless operation at all speeds.

Benefi ts from the Sulzer RT-fl ex system

At its heart, the Sulzer RT-fl ex engine is the same reliable, basic engine as the existing Sulzer RTA engine series. The power ranges, speeds, layout fields and full-power fuel

consumptions are the same for both engine versions.

For shipowners, the principal benefits of Sulzer RT-fl ex engines with their electronically-controlled common rail systems are:

• Reduced part-load fuel consumption

• Smokeless operation at all running speeds

• Very low, stable running speeds at about ten per cent nominal speed

• Easy engine setting for less maintenance

• Longer times between overhauls (TBO) expected, primarily through better load balance between cylinders and cleaner combustion at all loads.

Comments below are made on just the first three of the above points as these are the ones which have so far been definitely quantified.

Low exhaust emissions

A clearly visible benefit of Sulzer RT-fl ex engines is their smokeless operation at all ship speeds. It helps give a ‘green’ image.

This was well demonstrated in the testing of the first RT-fl ex engine and during the sea trials of the Gypsum Centennial.

The superior combustion performance with the common-rail system is achieved by maintaining the fuel injection pressure at the optimum level right across the engine speed range. In addition, selective shut-off of single injectors and an optimised exhaust valve timing help to keep smoke emissions below the visible limit at very low speeds.

The precision and flexibility in engine setting given by the RT-fl ex system facilitates compliance with the NOX regulation of Annex VI of the MARPOL 73/78 convention, usually referred to IMO NOX regulation.

The flexibility of the RT-fl ex engines will also allow a lowering of NOX emissions if the corresponding increase in BSFC is acceptable. With common-rail injection, a wide variety of injection patterns can be generated. The injected quantity of fuel can be divided, for pre-injection, triple injection, etc. The Sulzer RT-fl ex engine, with its individual fuel valve control, also has the unique ability to vary individually the injection timing and sequence between the three fuel injectors in each cylinder and thus to generate a tailor-made heat release.

In engine tests, this degree of flexibility has proved useful to reach NOX emissions of 20 per cent below the IMO NOX limit with a moderate BSFC increase of 2.3 per cent.

Very slow running

Sulzer RT-fl ex engines have also demonstrated their ability to run stably at very low speeds, lower than engines with mechanically-controlled injection. They can run without smoking at about ten per cent nominal speed. This makes for easy ship handling when manoeuvring or in river and canal passages.

Fig. 19: Sulzer RT-fl ex engines have the unique ability to shut off individual fuel injectors, here shown schematically. This feature is used to assure clean combustion for smokeless, stable running at very low speeds.

Such slow running was well confirmed in service in the Gypsum Centennial. Slow running was taken to a new ‘low’ during the testing in May/June 2004 of the first 12-cylinder RT-fl ex96C engine. Owing to its number of cylinders, it could run steadily at just seven revolutions per minute.

The very slow running is made possible by the precise control of injection, together with the higher injection pressures achieved at low speed, and shutting off injectors at low speeds. Reducing the number of injection valves in operation makes injection of the reduced fuel quantities more efficient, especially as the injection pressure is kept up to a higher value than in a mechanically-injected engine at the same speeds.

Shutting off injectors provides more stable operation with better distribution of engine load and thermal loads  than if very slow running was to be achieved by cutting out whole cylinders.

Shutting off injectors is enabled by the separate control of individual fuel injection valves. This feature is unique to Sulzer RT-fl ex engines. Usually the injection valves operate in unison but, as the engine speed is reduced, one injection valve can be shut off and at a lower speed a second injection valve can be shut off . Thus at minimum

speed, the engine runs on all cylinders but with just one injection valve in each cylinder.

If the RT-fl ex engine then runs for a period in singleinjector operation, the electronic control system switches between the three injection valves in a cylinder so that the thermal load is equalised around the combustion chamber.

Fuel consumption flexibility

Sulzer RTA engines have always been highly competitive in fuel consumption right across the load range owing to the use of variable injection timing (VIT). Variable exhaust valve closing (VEC) was also added in RTA84Tengines in 1991 to reduce further the part-load BSFC. These benefits have already been carried over to the electronically-controlled common-rail systems of the RT-fl ex engines.

At the first stage of development of RT-fl ex engines, however, the main objective has been to achieve the same performance standards as are achieved in the mechanical-camshaft engines, particularly with respect to power, speed, fuel consumption, exhaust emissions, cylinder pressures, etc. Thus the curves of brake specific fuel consumption (BSFC) of the first RT-flex engines have been the same as with corresponding RTA engines,or perhaps slightly lower in the part-load region. As the fuel injection pressure at part-load is kept higher with the common-rail injection system, combustion is sufficiently better to have a beneficial effect on fuel consumption in part-load operation.

Recently an alternative fuel consumption curve was introduced with Delta Tuning to provide even lower BSFC at loads less than 90 per cent full load. For both the original (Standard) and Delta Tuning curves, the RT-fl ex engines comply with the IMO NOX regulation. the shape of the new BSFC curve given by Delta Tuning. The BSFC is lowered in the mid- and low-load range, thereby increasing the NOX emission levels at those load points, but then has to

be increased at high engine loads (90–100 per cent load) for a compensating reduction in NOX levels.

Delta Tuning was first applied in the first Sulzer 8RT-fl ex96C engine which completed its official shop test on 9 April 2004.

Fig. 20: Sulzer 7RT-fl ex60C engine in Wärtsilä’s Trieste factory in October 2002. It develops 16,520 kW at 114 rpm, and  measures about 11.4 m long by 10.5 m high. Above the top platform, the rail unit covers can be seen open.

Common rail is now an industrial standard for diesel engines. It has been proven to be an tremendous step  forward for all sizes of diesel engines from automotive engines up to the largest low-speed two-stroke engines. In this environment, Sulzer RT-fl ex engines have become well accepted by shipowners. Shipowners’  confidence is being encouraged by the good operating experience with the growing number of RT-fl ex engines in service.

The combination of common-rail concepts and fully-integrated electronic control applied in Sulzer RT-fl ex engines clearly has excellent potential for future development. It gives the large degree of flexibility in engine setting and operation, together with reliability and safety, which are required to meet the challenges in future marine engine applications in terms of emissions control, optimized fuel consumption, insensitivity to fuel quality, ease of use, operational flexibility, etc.

Fig. 21: The world’s most powerful common-rail engine, the Sulzer 12RT-fl ex96C engine develops 68,640 kW at 102 rpm, and measures about 24 m long by 13.5 m high. It passed its official shop test in June 2004. The supply unit shown in figure 4 can be seen at the middle of the engine.

chapter-6

The major steps in two-stroke diesel technology have been surprisingly few over the past century: airless fuel injection in the 1930s, welded construction in the late 1940s, and   exhaust gas turbocharging and the use of heavy fuel oil both in the 1950s. Now  we have another major step – electronically controlled common-rail  fuel injection introduced in the Sulzer RT-flex engines.

Although common-rail fuel injection is itself not new, the addition of integral electronic control allows full use to be made of the flexibility possible with common-rail injection. Wärtsilä has therefore expanded the Sulzer RT-flex engine range to include cylinder bore sizes from 500 to 960 mm.

These are the most advanced low-speed marine engines available in the world today. The Sulzer RT-flex electronically controlled common-rail system has already been well described in recent issues of Marine News. However, we should note some key dates:

·         1981: First tests with electronically controlled fuel injection on a Sulzer low-speed engine, using individual, hydraulically operated fuel injection pumps.

·         1990 March: World’s first multicylinder electronically controlled uniflow two-stroke engine is started on the Winterthur test bed. Tested until 1995.

·         1993: Project started to develop the Sulzer RT-flex common-rail system.

·         1996: Component testing began for the Sulzer RT-flex common-rail system.

·         1998 June: Starting of the first Sulzer RT-flex full-scale engine on the Winterthur test bed.

·         2000 February: Order for the first series-built Sulzer RT-flex engine.

·         2001 January: Official shop test of the first series-built Sulzer RT-flex engine, the Sulzer 6RT-flex58T-B in Korea.

·         2001 September: Sea trials of the ‘Gypsum Centennial’ with the Sulzer

·         6RT-flex58T-B engine.

·         2002 October: Official shop test of the

first Sulzer RT-flex60C engine.The latest step in the above chronology is particularly significant because the Sulzer  RT-flex60C engine is the first large low-speed marine diesel engine designed

from the bedplate up solely as an electronically controlled engine with common-rail fuel injection. In fact, it is not available in any other form.

The Sulzer RT-flex60C

The market need for a new Sulzer two-stroke engine design in the region of 600 mm bore was seen a few years ago when an increasing number of container liners of 5500 TEU capacity or larger were being ordered. It was evident that there would be a growing market for container feeder vessels to serve these larger container liners, and also that the sizes of the feeder vessels themselves would tend to become  larger, perhaps in the capacity range of 1200-3000 TEU. Market research among shipowners and  shipbuilders showed that the various sizes of feeder vessels would need compact  engines in the power range of around 12,000 to 19,000 kW for the envisaged  range of ship speeds. There was clearly a need for more power than is available from the Sulzer RTA62U-B type, and with a higher shaft speed than the Sulzer RTA58T-B engine type.

Thus the decision was made to introduce the Sulzer RT-flex60C which would cover the required power range with

five to eight cylinders at an output of  2360 kW/cylinder. The nine-cylinder model was added later to extend the power  range to 21,240 kW. The rotational speed selected, 114 rpm, is a little faster than  would be ideal hydrodynamically for  suitable propellers but it was selected as the best fit between the priorities of operating and manufacturing costs.

The first pair of Sulzer RT-flex60C engines were specified by Agricultural Export Co (Agrexco) and Münchmeyer, Petersen GmbH & Co KG for the propulsion of two 13,200 dwt containerized reefers contracted in Portugal  towards the end of 2000. Each seven-cylinder Sulzer RT-flex60C engine  has a maximum continuous power of 16,520 kW at 114 rpm.

The engines were built at Wärtsilä’s  Trieste factory. The first engine completed its official shop test on 14-15 October 2002.

The second engine successfully passed a type approval test on 17-20 December 2002. This test was witnessed by the  representatives of the classification societies, as well as the shipowners and shipbuilder.

Four similar Sulzer 7RT-flex60C engines are also being built under licence at Hyundai Heavy Industries Ltd in Korea for four 30,000 dwt multipurpose carrierscontracted at Shanghai Shipyard in China by Chinese-Polish Joint Stock Shipping Co (Chipolbrok).

The first two of these engines  successfully passed their official shop tests on 22-28 January and 6-7 March 2003.

Testing Sulzer RT-flex60C engines

The four Sulzer RT-flex60C engines so far tested have been put through the usual test programmes for new engine types.

For all four engines, initial tests runs were employed to optimize the turbocharging and fuel injection equipment. The usual test measurements were taken as for all production engines to con firm their predicted performance in terms of power, speed, fuel consumption, etc.

However, the first two engines were subjected to further tests withmeasurements of component stresses and temperatures to confirm design calculations.

This can be illustrated by the combustion space which, for the Sulzer RT-flex60C, follows well-established Sulzer RTA practice. All the surrounding components are bore-cooled. The piston crown employs the usual jet-shaker oil cooling principle with an arrangement of cooling bores in the crown so that the surface temperatures of the crown are moderate with a very even distribution.

An important part of the test programmes was final adjustment and thorough testing of the RT-flex systems, particularly of their electronic control system.

During the tests, the four engines all  performed as expected. The electronic systems were noticeably stable. The engines could be started, stopped, manoeuvred, taken up to load and unloaded without any hindrance.

Type approval for RT-flex system

The Sulzer 6RT-flex58T-B engine of the Gypsum Centennial entered service with individual approval for the RT-flex system from the classification society Lloyd’s Register of Shipping. However, following the successful type approval test of the second Trieste-built Sulzer RT-flex60C engine in October 2002, the RT-flex system has received full classification society approval for general application in ships.

RT-FLEX service experience

In parallel with the building and testing of  the Sulzer RT-flex60C, service experience has been accumulating with the first  RT-flex engine. This is a Sulzer 6RT-flex58T-B engine which passed its official shop test in January 2001 and is installed in the 47,950 dwt bulk carrier Gypsum Centennial. The ship was built for her owners Gypsum Transportation Ltd (GTL) of Bermuda by Hyundai MipoDockyard in Ulsan, Korea. The Sulzer  RT-flex main engine has a maximum continuous output of 11,275 kW at 93 rpm.

The ship was delivered in September 2001 and the service experience with the engine has since been very good, with currently more than 8000 hours’ operation.

This Sulzer 6RT-flex58T-B is the world’s first series-built large low-speed engine with electronically controlled common-rail fuel injection. It must be remembered that this engine was built to operate using only the electronically controlled common-rail system with no alternative. It went to sea as a fully  industrialized product capable of continuous heavy-duty commercial operation. After some ‘teething problems’ were satisfactorily solved, the engine achieved this performance with very good success.

In October 2002, the engine  was inspected in Tampa, Florida, as part of the ship’s guarantee  ocking after her first year’s service, 5295 running hours. The engine was found to be in good condition. The few shortcomings could all be corrected. The RT-flex system was thoroughly inspected to assess the condition of all hardware. Certain components were  exchanged for later detailed inspection.

The opportunity was also taken to exchange components for new, improved designs where  appropriate. For example, the control oil pumps which had failed in service were replaced by a new design, and  given elastic mountings and flexible hoses.

The roller guide of a fuel pump was found to be seized. The problem was insufficient clearance between the roller guide and its casing. These components were thus renewed. This and previous exchanges meant that all fuel pumps were  then of fully modified design. Since the guarantee docking, the RT-flex engine has run well, behaving much as it had done during the months immediately before the docking inspection.

RT-flex programme extension

The excellent experience with the Sulzer  RT-flex system, in the research engine since June 1998, in the shop testing of now two Sulzer 6RT-flex58T-B and four Sulzer 7RT-flex60C engines, and in the shipboard  service of the first 6RT-flex58T-B since September 2001, has encouraged Wärtsilä to extend the Sulzer RT-flex engine programme to both lower and higher powers. The objective is to offer a comprehensive programme of low-speed engines with electronically controlled common-rail systems.

Sulzer RT-flex50

Following the RT-flex58T-B and RT-flex60C engines, the first addition to the programme is the new Sulzer RT-flex50  engine which is currently being developed. The Sulzer RT-flex50 is being adapted by Wärtsilä from the conventional Sulzer RTA50 engine with camshaft-based fuel injection, etc., which is being jointly developed by Wärtsilä and Mitsubishi Heavy Industries Ltd.

Of 500 mm bore by 2050 mm stroke, the RT-flex50 has a maximum continuous power of 1620 kW/cylinder at 124 rpm. With five to eight cylinders, it will cover a power range of 5650-12,960 kW at 99 to 124 rpm. It thus offers the right powers and speeds for a wide variety of ship types including the new generation of Handymax and Panamax bulk carriers, large product tankers, container feeder vessels and medium-sized reefer ships.

The first Sulzer RT-flex50 engine is  scheduled to begin testing in the fourth quarter of 2004.

Sulzer RT-flex96C and RT-flex84T-D

The RT-flex concept will also be extended to the highest powers with the Sulzer RT-flex96C and  RT-flex84T-D engines. The Sulzer RTA96C engine type has been popular for the propulsion of container liners. A total of 139 RTA96C engines are now in service or on order.

They currently extend from 7-cylinder engines of 40,040 kW in 3000 TEU ships to the 68,640 kW 12-cylinder engines for the largest ships of more than 8000 TEU.

The Sulzer RTA84T engine type is  employed solely for the propulsion of VLCCs and ULCCs, predominantly in the 7-cylinder model. The current Sulzer 7RTA84T-D gives 28,700 kW.

The benefits of the RT-flex engines – smokeless operation, better fuel economy, reduced maintenance and lower steady  running speeds – will certainly be attractive for both types of ship.

The first Sulzer RT-flex96C engine is  scheduled for shop testing in April 2004, with delivery in the ship towards the end of 2004. The first RT-flex84T-D can be built in mid-2005, according to market requirements.

Chapter-7

Environmental Friendly Two-stroke Marine Diesel Engine,

“MITSUBISHI UEC Eco-Engine”

The environmental friendly diesel engine, “UEC Eco- Engine” is named for the letters of “Eco” which are found in its design goals of Ecology, Excellent engine Condition, Easy Control, and Economy, all by Electronic Control,.

The UEC Eco-Engine is an engine that has been developed by modifying a conventional engine, of which fuel injection system, exhaust valve driving system, engine starting system, and cylinder lubricating system are controlled electronically. As a result, the engine structure is much simplified by eliminating the conventional large mechanical parts, such as cams, camshaft, and driving gears. The modification and conversion to an electronic control system makes it possible to adjust optimal timing of the fuel injection and exhaust valve actuating and fuel injection rate according to the engine operating condition, ambient conditions, and fuel properties. As a result, engine performance can be optimized across the entire load range.

Therefore, the consumption of fuel oil and  cylinder lubricating oil are both reduced as a result, the emission characteristic with regards to NOX and smoke can be improved. Higher reliability of the combustion chamber can be ensured by the optimization of the operation condition, and the higher economical operation can be achieved. Furthermore, since the starting performance is improved and an extremely lower revolution operating can be achieved by the realization of better maneuvering capability.

Fig. 1 Fundamental structure of engine

The UEC Eco-Engine will be a leading engine in the next generation, which has the above-mentioned various advantages in addition to the highly economy and highly reliability that has been proven on the conventional UEC engines.

3. Overview of electronic control system

3.1 Fuel injection system

Fig. 2 shows the configuration of the fuel injection system. The fuel injection system consists of pilot solenoid valve, main valves, fuel injection pump, and fuel injection valves. The pilot solenoid valve consists of a main solenoid valve and sub solenoid valve. The fuel injection rate can be controlled by actuating the main and sub solenoid valves at different times. As a result, the initial combustion temperature is reduced making it possible to reduce NOX emission, compared with the conventional engines.

Usually there is trade-off relationship between fuel oil consumption and NOX emission . The UEC Eco-Engine is able to reduce NOX emissions by about 10 to 15% compared with conventional engines, at same fuel oil consumption levels, when priority is given to the NOX mode. On the other hand, fuel oil consumption can be reduced by 1 to 2%, at the same NOX emission levels, when priority is given to fuel oil consumption. In addition, in the UEC Eco-Engine, the operation mode can easily be switched at the control panel, so that it becomes possible to choose the optimal operation at any condition.

In the conventional engines, fuel injection pressure gets lower at low load operation since it depends on the rotational speed of the engine. On the other hand, in the UEC Eco-Engine, since the fuel injection is performed using high-pressure hydraulic oil throughout the entire load range, fuel injection pressure is maintained at nearly maximum levels, even under low loads. Therefore, appropriate injection pressure improves combustion condition at lower load and reduces smoke emission significantly  

Fig. 2 Configuration of fuel injection system         Fig. 4 Relation between fuel oil consumption and NOx emission

3.2 Exhaust valve driving system 

The configuration of the exhaust valve driving system is shown in Fig. 6 .

The exhaust valve driving system consists of a pilot solenoid valve, main valves, lower actuating unit, upper actuating unit, and exhaust valve. The timing of the opening of the exhaust valve can be optimized by adopting an electronic control system throughout the entire load range. Accordingly, the timing for opening the exhaust valve can be delayed by increasing the velocity of the opening, so that the effective work of the piston can be increased.

These optimizations result in an improvement in fuel oil consumption of approximately 1 to 2%, compared with the conventional engines.

Electronic control

Fuel injection, exhaust valve actuating, and starting air  systems are controlled electronically and are optimized for all  operation loads.

Ecology

NOx emission can be reduced and smokeless operation achieved. In addition, water injection system, a drastic NOx reduction technology, may be applied in combination with the Eco-system to cope with the stricter NOx emission regulations anticipated in the future.

Economy

Lower specific fuel oil consumption especially in partial loads can be obtained, and this can lead to less running cost.

Easy control

Eco-Engine assures stable low load operation with good engine performance. Easy change of operating modes and fine tuning of operating conditions are also possible during operation.

2.5 Excellent engine condition (higher reliability)

Appropriate fuel injection pressure and optimum injection timing, which are the most favorable for combustion conditions at each load, can further enhance the reliability of  the hot components proven in UEC conventional engine.

1. HISTORY OF UEC ECO-ENGINE PROJECT

Anticipating possible future requirements, we began to study various solutions as early as 1988.  Over a long period, the fundamental system has been verified on single cylinder research engines, the NC45 (45 cm bore) and the NC33 (33 cm bore) at the MHI Nagasaki  Research & Development Center. The first generation of the electronic system was tested on the NC45 research engine from 1988 to 1993, and more than 1,200 hours of various operations verified the system’s performance and reliability. The test results satisfied the concepts of the system. The second generation of the electronic system followed on the NC33 research engine and was tested until 1997. Its results boosted our belief that an electronically controlled engine has advantages to comply with future industry requirements. Figure 1 shows the NC33 research engine.

Based on the above-mentioned good experimental results, UEC Eco-Engine project started in early 2000 to meet the growing market demand. The 7UEC33LS Ⅱ engine, a stationary diesel engine generating set at the MHI Kobe Shipyard & Machinery Works, was converted to the first full-scale Eco-Engine in December 2001 and has proved its reliability through three years of various operations. In this engine, the electronic control system was retrofitted to a conventional engine. The aspects of the engine can be seen in Figure 2. The main particulars of the engine are listed in Table 1.

Retrofitted electronic-control device view from driving end

Fig. 1 NC33 research engine at MHI Nagasaki  Research & Development Center

|

view from fore end

Fig. 2 7UEC33LSII-Eco at MHI Kobe

Shipyard and Machinery Works

As mentioned above, we concentrated on the reliability and performance of the electonically controlled engine through a long span of verification tests and successfully confirmed high reliability as well as high performance. We will introduce the first commercial project of UEC Eco-Engine in a later section.

4. MHI’S LOW EMISSION TECHNOLOGY

Fig. 3 Applications to low NOx emission technology

In general, our technological plans to cope with further strict NOx regulations are described in Figure 3. To comply with the International Maritime Organization’s (IMO) first regulation, which took effect in May 2005, we have already delivered all our engines in compliance with the regulation by optimization of the fuel injection nozzle and fine tuning of our traditional engines.

To satisfy the second regulation, which is estimated to be 20 to 30% stricter than the first regulation, we plan to apply UEC Eco-Engine or a water injection system in combination with a conventional engine. To satisfy the third regulation, we will combine UEC Eco- Engine with a water injection system. According to the severity of the regulations, other technologies might be needed, for example, the Selective Catalytic Reactor (SCR).

Anticipating future demand, we will maintain our efforts to develop the necessary technologies.

5. FUNDAMENTAL STRUCTURE

The engine’s fundamental structure is seen in Figure 4, where it is compared with a conventional engine.

Fig. 4 Fundamental structure of engine

By electronic control, engine structure is greatly simplified by eliminating such conventional large mechanical parts as the fuel and exhaust cams, the camshaft, and the driving gears. An electronic control system with a hydraulic oil supply system is added. Accordingly, maintenance on these mechanical components is also eliminated, and the computational tuning of engine operating conditions also eliminates the delicate  adjustment work on these parts both in the shop and on board.

Simple fine tuning of operating conditions are possible during operation, this means that engine operation will be much more flexible than conventional engine.

An overview of the fuel injection and exhaust valve actuating mechanisms are described in Figure 5. The fuel injection pump and the lower exhaust valve  driving gear are actuated by 320 bar hydraulic oil. This pressurized oil is accumulated in the accumulator block  mounted at each cylinder. The connection blocks are applied

Fig. 5 System overview of cylinder component

The hydraulic power for fuel injection and exhaust valve actuation is controlled by an on/off type solenoid valve unit and an engine control system. The timings of fuel injection and exhaust valve open/close are also controlled electronically to achieve the best condition for any operation mode. This concept simplifies readjustments needed to maintain better operating conditions.

Downstream from the fuel injection pump and the lower exhaust valve driving gear, the same design concepts of the conventional system are applied to reduce crew education for new maintenance work about such components

6. FUEL INJECTION SYSTEM

Figure 6 shows a cross section of the fuel injection system for UEC Eco-Engine. The fuel injection pump has a similar structure to the conventional mechanical models but is rather simplified. This means that the crew is already familiar with maintenance for the fuel injection pump, reducing overhaul time.

Fig. 6 Fuel injection system

As one of its main features, two sets of on/off type solenoid  valves are mounted to control the injection pattern, which depends on the operating load, and to improve the trade-off relationship between thermal efficiency and NOx emission.

The mechanism to change the fuel injection pattern is shown in Figure 7. This is our patented technology put into practice by a pair of on/off type solenoid valves.

Fig. 7 Controlled fuel injection pattern

In addition, we are now incorporating a water injection system with Eco-Engine to comply with future anticipated  stricter NOx emission regulations.

A feedback control function is applied to control the fuel injection volume to compensate for the equivalent thermal load and individual cylinder control. Fuel pump stroke is monitored by twin gap sensors at each cycle. This emphasizes the system’s reliability through observation of the control system.

7. EXHAUST VALVE ACTUATING SYSTEM

Figure 8 shows a cross section of the exhaust valve actuating system for UEC Eco-Engine.

The exhaust valve open and close timings are also controlled by electronic control system using the on/off solenoid valve unit. Accordingly, timings are optimized depending on the operating load. For precise timing control, a feedback control function is applied by observation of the exhaust valve lift.

The actuating mechanism is similar to conventional mechanical ones and inherits their reliability and method of maintenance.

Fig. 8 Exhaust valve actuating system

8. CONTROL VALVE UNIT

Solenoid valve units are key components of an electronically controlled engine. The valve units of a large electronically controlled engine require very quick response, high flow rate, and long life cycle. We started valve development in 1999 and have already confirmed its performance.

The most important issue is reliability for a long life cycle. Thus, endurance tests were undertaken. The endurance test of valve unit finished 300 million cycle that corresponds to approximately six years of actual operation on board, and it satisfied its requirements.

The small size unit for a bore 40 cm class engine has also been verified in the 7UEC33LS Ⅱ -Eco prototype. The performance and endurance of the medium size unit for a bore 60 cm class engine were verified by a test bench similar to the fuel injection system in Figure 9.

Fig. 9 Control valve unit on test bench

9. STARTING AIR SYSTEM

Figure 10 compares the starting air systems. The conventional starting air control valve is eliminated, and solenoid valves and a control air pipe are added. The starting  valves are electronically controlled to achieve better performance and flexibility for engine start and crash astern.

Fig. 10 Comparison of starting air systems

10. HYDRAULIC OIL SUPPLY SYSTEM

A hydraulic oil supply system (see Figure 11) is another key component of Eco-Engine.

11. ECO-ENGINE CONTROL SYSTEM

An engine control system is prepared for the Eco Main Controller (EMC) and installed in the control room to interface with the Remote Control System. The Local Control Box (LCB) and the Eco Cylinder Controller (ECC) are mounted on the engine. These controllers are connected by a  duplicated network line. An overview of the control system is provided in Figure 12.

Fig. 12 Control system overview

11.1 EMC

For duplication purposes, the controller is comprised of two units operating parallel and performing the same task;  they are duplicates of each other. If the active EMC fails, the other unit will assume control without any interruption.

EMC performs the following tasks:

• Speed governor functions
• Start/stop sequences
• Timing control of fuel injection, exhaust valve actuation,

and starting air systems

·                      Control of the hydraulic oil supply system

·                      Alternative operation and control modes

·                      Network functions

·                      Malfunction observation of entire control system

11.2 ECC

Each ECC, which is mounted on individual cylinder,  performs the orders for the timing of fuel injection, exhaust valve actuating, and starting air systems.

11.3 LCB

This controller provides engine side control for emergency  if the Remote Control System or both EMCs fail. This means that the operator can choose two operations, which are controlled by EMC or LCB.

We developed an evaluation tool called the Real Time Simulator (RTS), as shown in Figure 13, that verifies control sequences by simulating such engine running conditions as start/stop, crash astern, rough seas, and malfunctions. The image of this tool creates a virtual engine in the simulator.

We verified the first commercial control system by using this tool before running it in our shop. In addition, the reliability of the control system’s hardware was evaluated against surrounding conditions, including vibration, temperature, and noise.

12. THE FIRST COMMERCIAL ECO-ENGINE

In June 2004, the manufacture of the first commercial UEC Eco-Engine, 8UEC60LSⅡ-Eco, was completed. Its main particulars are listed in Table 2. Figures 14 and 15 show pictures of the engine in our shop. Its comprehensive tests were carried out in our shop for three months in 2004, and a sea trial was held in May 2005. This section introduces their major results.

Table 2 Main particulars of 8UEC60LSⅡ-Eco

12.1 Economy and Low emission mode

We evaluated actual operating conditions by applying fuel injection controls. To operate Low Emission Mode, NOx emission reduction can be obtained at the same SFOC. On the other hand, to select Economy Operating Mode, SFOC can be reduced 1 to 2% compared with conventional engines. The  engine operation mode can be easily changed over by a switch on the controller.

From the results of 8UEC60LSⅡ-Eco shop tests, we found that trade-off between thermal efficiency and NOx emission can be improved as we planned. Figure 16 compares SFOC and NOx emission between fuel injection controls ON and OFF in normal load. With fuel injection control, we achieved Δ 10.2% NOx emission in equivalent SFOC.

Fig. 16 Improvement by fuel injection control

12.2 Engine Performance

Figure 17 shows the performance curve of 8UEC60LSⅡ- Eco with the test results of economy and low emission modes. As expected, especially in lower loads, economy mode decreases SFOC, and low emission mode decreases NOx emission.

Fig. 17 Performance curve of 8UEC60LSⅡ-Eco

12.3 Smoke

The fuel injection system is significantly improved with electronic control system. Thus, smokeless operation can be achieved for whole operation load. Figure 18 compares the Bosch Smoke Number measured on 8UEC60LSII-Eco.

Fig. 18 Smoke measurement results of 8UEC60LSⅡ-Eco

12.4 Cylinder lub. oil consumption

Eco-Engine has electronically controlled cylinder lubricating system to obtain precise injection quantity and optimum injection timing at each load, which lead to higher reliability on piston rings and cylinder liner and lower operation costs. Figure 19 shows the transition of lubrication oil feed rate of 8UEC60LSⅡ-Eco in shop tests. At the end of shop tests, feed rate decreased less than 1.0 g/PSh.

Fig. 19 Lub. oil feed rate on shop test

12.5 Inspection results

Inspection results after sea trials revealed that each part was maintained in excellent condition. Figures 20 and 21  show inspection results.

Fig. 20 Inspection results after sea trial (1)

(d) Cylinder Liner

Fig. 21 Inspection results after sea trial (2)

13. SUMMARY OF ADVANTAGES

As a summary, the distinctive advantages of UEC Eco-Engine are as follows:

13.1 Environmental friendliness

Smokeless operation can be achieved by appropriate fuel injection pressure at any load. Reduction of NOx emission can be obtained by tuning the fuel injection timing and pattern at any load.

13.2 Lower Specific Fuel Oil Consumption (SFOC)

The timing of fuel injection and exhaust valve actuation can be flexibly optimized by electronic control according to engine operating loads, atmospheric conditions, and fuel oil properties. Accordingly, lower SFOC can be obtained, especially in partial loads.

13.3 Easy control (better maneuverability)

Eco-Engine assures stable continuous low load operation, even for extremely low loads, with good engine performance ecause of improved combustion conditions thanks to appropriate fuel injection pressure and optimized fuel injection timing and exhaust valve actuating in lower loads.

13.4 Higher reliability

In Eco-Engine, appropriate fuel injection pressure, which is the most favorable for combustion conditions at any load, will urther enhance the high reliability of the hot components proven on conventional UEC engines, such as piston crown,piston ring, cylinder liner, and exhaust valve.

13.5 Flexible operation

Easy changes of operating modes and fine tuning of operating conditions are possible during operation.

13.6 Less maintenance

With electronic control system, the engine structure is significantly simplified by eliminating conventional large mechanical parts. Accordingly, maintenance on these mechanical components is eliminated, and the computational tuning of engine operating conditions obviates the need for delicate adjustment work on these parts both in the shop and onboard.

Chapter-8

WARTSILA DUEL FUEL ENGINES

Dual-fuel engines:

Ø  Gas engine technologiesGas-diesel, spark-ignition gas and dual-fuel engines

Ø  Dual-fuel engine applicationsOn land, at sea and in LNG carriers

Ø  Dual-fuel engine parametersWärtsilä 32DF, 34DF and Wärtsilä 50DF

Ø  Dual-fuel engine systemsGas fuel, pilot fuel

Ø  Future LNG fueled vessels

Gas engine technologies

Gas-diesel (GD) engines:

Ø  Runs on various gas / diesel mixtures or alternatively on diesel.

Ø  Combustion of gas, diesel and air mixture in Diesel cycle.

Ø  High-pressure gas injection.Spark-ignition gas (SG) engines:

Ø  Runs only on gas.

Ø  Combustion of gas and air mixture in Otto cycle, triggered by spark plug ignition.

Ø  Low-pressure gas admission.

Dual-fuel (DF) engines:

Ø  Runs on gas with 1% diesel (gas mode) or alternatively on diesel (diesel mode).

Ø  Combustion of gas and air mixture in Otto cycle, triggered by pilot diesel injection (gas mode), or alternatively combustion of diesel and air mixture in Diesel cycle (diesel mode).

Ø  Low-pressure gas admission.

v  Engine performance

v  Higher output

v  Gas system

v  Double wall gas piping

v  Lubricating oil system

v  Components built on engine

v  Compressed air system

v  Direct air injection into cylinders

v  Charge air and exhaust gas system

v  SPEX system

v   Automation system

v  UNIC engine control system

IMO NOx–Regulation 13

•New buildings (diesel engines > 130 kW): Tier II from 2011; Tier III to be applied in designated areas from 2016* (Tier II to be applied outside these areas)

•Existing ships: Tier I to be applied for vessels constructed between 1990 and 2000 (diesel engines > 5000 kW and > 90 liters / cylinder). Some exemptions are considered

IMO SOxand PM –Regulation 14

v   Low Natural Gas Emissions 25-30% lower CO2

v  Low Carbon to Hydrogen ratio of fuel 85% lower NOX

v  Lean burn concept (high air-fuel ratio) No SOXemissions

v  Sulphur is removed from fuel when liquefied  50% lower PM Particulates

v  Particulates vary across operating range No visible smoke No sludge deposits extends engine life

Emission comparison

Dual-Fuel engine application: conclusions

Ø LNG utilized as marine fuel is cost competitive

Ø Technology is already available and well proven in the marine market

Ø Dual-Fuel Engines represent the emission reduction state of art technology in the marine field

CHAPTER-9

LNG Carriers with ME-GI Engine and

High Pressure Gas Supply System

The demand for larger and more energy  efficient LNG carriers has resulted in rapidly increasing use of the diesel engine as the prime mover, replacing traditional steam turbine propulsion plants.

A  low speed direct propulsion alternative, using a dual-fuel two-stroke engine, is now also available:

High thermal efficiency, flexible fuel/ gas ratio, low operational and installation costs are the major benefits of  this alternative engine version

The engine utilises a high-pressure gas system to supply boil-off gas at pressures of 250-300 bar for injection into the cylinders.

Apart from the description of the fuel gas supply system, this paper also discusses  related issues such as requirements for classification, hazardous identification procedures, main engine room safety, maintenance requirements and availability.

It will be demonstrated that the ME-GI based solution has operational and economic benefits over other low speed based solutions, irrespective of vessel size, when the predicted criteria for relative energy prices prevail.

ME-GI Gas System

Engineering

The ME-GI engine series, in terms of engine performance (output, speed, thermal efficiency, exhaust gas amount and temperature, etc.) is identical to the well-established, type approved ME engine series. The application potential for the ME engine series therefore also applies to the ME-GI engine, provided that gas is available as a main fuel. All ME engines can be offered as ME-GI engines. Since the ME system is well known, the following description of the ME-GI  engine design only deals with new or modified engine components. Fig. 9 shows one cylinder unit of a S70ME-GI, with detail of the new modified parts. These comprise gas supply double-wall piping, gas valve control block with internal accumulator on the (slightly modified) cylinder cover, gas injection valves and ELGI valve for control of the injected gas amount. In addition,

there are small modifications to the exhaust gas receiver, and the control and manoeuvring  system.

Apart from these systems on the engine, the engine and auxiliaries will comprise some new units. The most important ones, apart from the gas supply system, are listed below, and the full system is shown in schematic form in Appendix IV The new units are: Ventilation system, for venting the space between the inner and outer pipe of the double-wall piping.  Sealing oil system, delivering sealing oil to the gas valves separating the control oil and the gas. Inert gas system, which enables purging of the gas system on the engine with inert gas.

The GI system also includes:

Control and safety system, comprising a hydrocarbon analyser for checking the hydrocarbon content of the air in the double-wall gas pipes.

The GI control and safety system is designed to “fail to safe condition”. All failures

detected during gas fuel running including failures of the control system itself, will result in a gas fuel Stop/Shut Down, and a change-over to HFO fuel operation.

Blow-out and gas-freeing purging of the high-pressure gas pipes and the complete gas supply system follows. The changeover to fuel oil mode is always done without any power loss on the engine.

The high-pressure gas from the compressor unit flows through the main pipe via narrow and fl exible branch  pipes to each cylinder’s gas valve block and accumulator. These branch pipes  perform two important tasks:

They separate each cylinder unit from the rest in terms of gas dynamics, utilizing the well-proven design philosophy  of the ME engine’s fuel oil system.

They act as flexible connections between the stiff main pipe system and the engine structure, safeguarding  against extra-stresses in the main and branch pipes caused by the inevitable differences in thermal expansion of the gas pipe system and the engine

structure.

The buffer tank, containing about 20 times the injection amount per stroke at MCR, also performs two important tasks:

It supplies the gas amount for injection at a slight, but predetermined, pressure drop.

It forms an important part of the safety system.

Since the gas supply piping is of common rail design, the gas injection valve must be controlled by an auxiliary control oil system. This, in principle, consists of the ME hydraulic control (system) oil system and an ELGI valve, supplying highpressure control oil to the gas injection valve, thereby controlling the timing and opening of the gas valve.

ME-GI Injection System

Dual fuel operation requires the injection  of both pilot fuel and gas fuel into the combustion chamber.

Different types of valves are used for this purpose. Two are fitted for gas injection and two for pilot fuel. The auxiliary media required for both fuel and gas operation are as follows:

High-pressure gas supply

Fuel oil supply (pilot oil)

Control oil supply for activation of gas injection valves

Sealing oil supply.

The gas injection valve design is shown in Fig. 10. This valve complies with traditional design principles of compact  design. Gas is admitted to the gas injection valve through bores in the cylinder cover. To prevent gas leakage between cylinder cover/gas injection  valve and valve housing/spindle guide, sealing rings made of temperature and

gas resistant material are installed. Any gas leakage through the gas sealing  rings will be led through bores in the  gas injection valve and further to space between the inner and the outer shield   pipe of the double-wall gas piping system. This leakage will be detected by HC sensors.

The gas acts continuously on the valve spindle at a max. pressure of about 250 bar. To prevent gas from entering  the control oil activating system via the clearance around the  spindle, the spindle is sealed by sealing oil at a pressure higher than the gas pressure

(25-50 bar higher).

The pilot oil valve is a standard ME fuel  oil valve without any changes, except for the nozzle. The fuel oil pressure is constantly monitored by the GI safety system, in order to detect any malfunctioning of the valve.

Fig. 10: Gas injection valve – ME-GI engine

The designs of oil valve will allow operation solely on fuel oil up to MCR. lf the customer’s demand is for the gas engine to run at any time at 100 % load on fuel oil, without stopping the engine, this can be done. If the demand is prolonged operation on fuel oil, it is recommended to change the nozzles and gain an increase in effi ciency of around  1% when running at full engine load.

Fig. 11: ME-GI system

As can be seen in Fig. 11 (GI injection system), the ME-GI injection system consists of two fuel oil valves, two fuel gas valves, ELGI for opening and closing of the fuel gas valves, and a FIVA valve to control (via the fuel oil valve) the injected fuel oil profi le. Furthermore, it consists of the conventional fuel oil pressure booster, which supplies pilot oil in the dual fuel operation mode. This fuel oil pressure booster is equipped

with a pressure sensor to measure the pilot oil on the high pressure side. As mentioned earlier, this sensor monitors the functioning of the fuel oil valve. If any deviation from a normal injection is found, the GI safety system will not allow opening for the control oil via the ELGI valve. In this event no gas injection will take place.

Under normal operation where no malfunctioning of the fuel oil valve is found, the fuel gas valve is opened at the correct crank angle position, and gas is injected. The gas is supplied directly into an ongoing combustion. Consequently the chance of having unburnt gas eventually slipping past the piston rings and into the scavenge air receiver

is considered to be very low. Monitoring the scavenge air receiver pressure safeguards

against such a situation. In the event of high pressure, the gas mode is stopped and the engine returns to burning fuel oil only.

The gas flow to each cylinder during one cycle will be detected by measuring the pressure drop in the accumulator. By this system, any abnormal gas flow, whether due to seized gas injection valves or blocked gas valves, will be detected immediately. The gas supply will be discontinued and the gas lines purged with inert gas. Also in this

event, the engine will continue running on fuel oil only without any power loss.

High-Pressure Double-Wall Piping

A common rail (constant pressure) gas supply system is to be fitted for high pressure

gas distribution to each valve block. Gas pipes are designed with double-walls, with the outer shielding pipe designed so as to prevent gas outflow to the machinery spaces in the event of rupture of the inner gas pipe.

The intervening space, including also the space around valves, flanges, etc., is equipped with separate mech-anical ventilation with a capacity of approx. 30 air changes per hour. The pressure in the intervening space is below that of the engine room with the (extractor) fan motors placed outside the ventilation ducts. The ventilation inlet air is taken from a non-hazardous area.

Gas pipes are arranged in such a way, see Fig. 12 and Fig 13, that air is sucked into the double-wall piping system from around the pipe inlet, from there into the branch pipes to the individual gas valve control blocks, via the branch supply pipes to the main supply pipe, and via the suction blower into the atmosphere. Ventilation air is exhausted to a fi re-safe place. The double-wall piping system is designed so that every part is ventilated.

All joints connected with sealings to a high-pressure gas volume are being ventilated. Any gas leakage will therefore be led to the ventilated part of the double-wall piping system and be detected by the HC sensors.

The gas pipes on the engine are designed for 50% higher pressure than the normal working pressure, and are supported so as to avoid mechanical vibrations. The gas pipes are furthermore shielded against heavy items falling down, and on the engine side they are placed below the top-gallery. The pipes are pressure tested at 1.5 times the working pressure. The design is to be all-welded, as far as it is practicable, using flange connections only to the extent necessary for servicing purposes.

Fig. 12: Branching of gas piping system

Fig. 13: Gas valve control block

Ventilation air

The branch piping to the individual cylinders is designed with adequate flexibility to cope with the thermal expansion of the engine from cold to hot condition. The gas pipe system is also designed so as to avoid excessive gas pressure fluctuations during operation.

For the purpose of purging the system after gas use, the gas pipes are connected to an inert gas system with an inert gas pressure of 4-8 bar. In the event of a gas failure, the high-pressure pipe system is depressurised before automatic purging. During a normal gas stop, the automatic purging will be started after a period of 30 min. Time is

therefore available for a quick re-start in gas mode.

Fuel Gas System -

Control Requirements

The primary function of the compressor control system is to ensure that the required discharge pressure is always available to match the demand of the main propulsion diesel engines. In doing so, the control system must adequately handle the gas supply variables such as tank pressure, BOG rate (laden and ballast voyage), gas composition and gas suction temperature.

If the amount of nBOG decreases, the compressor must be operated on part load to ensure a stable tank pressure, or forced boil-off gas (fBOG) added to the gas supply. If the amount of nBOG increases, resulting in a higher than acceptable tank pressure, the control system must act to send excess gas to

the gas combustion unit (GCU).

Tank pressure changes take place over a relatively long period of time due to the large storage volumes involved.

A fast reaction time of the control system is therefore not required for this control variable.

The main control variable for compressor operation is the feed pressure to the ME-GI engine, which may be subject to controlled or instantaneous change. An adequate control system must be able to handle such events as part of the “normal” operating procedure.

The required gas delivery pressure varies between 150-265 bar, depending on the engine load (see Fig. 14 below).

Fig. 14: Gas supply station, guiding specifi cation

The compressor must also be able to operate continuously in full recycle mode with 100 % of delivered gas returned to the suction side of the compressor. In addition, simultaneous delivery of gas to the ME-GI engine and GCU must be possible.

When considering compressor control, an important difference between centrifugal and reciprocating compressors should be understood. A reciprocating compressor will always deliver the pressure demanded by the down-stream user, independent of any suction conditions such as temperature, pressure, gas composition, etc. Centrifugal compressors are designed to deliver a certain head of gas for a given flow. The discharge pressure of these compressors will therefore vary according to the gas suction condition.

This aspect is very important when considering transient starting conditions such as suction temperature and pressure. The 6LP250-5S_1 reciprocating compressor has a simple and fast startup procedure.

Compressor control – 6LP250-5S_1 Overall control concept

Fig. 15 shows a simplified view of the compressor process flow sheet. The system may be effectively divided into a low-pressure section (LP) consisting of the cold compression stage 1, and a high-pressure section (HP) consisting of stages 2 to 5.

The main control input for compressor control is the feed pressure P set required by the ME-GI engine. The feed pressure may be set in the range of 150 to 265 bar according to the desired engine load. If the two ME-GI engines are  operating at different loads, the higher set pressure is valid for the compressor control unit.

If the amount of nBOG is insufficient to satisfy the engine load requirement, and make-up with fBOG is not foreseen, the compressor will operate on part load to ensure that the tank pressure remains

within specified limits. The ME-GI engine will act independently to increase the supply of HFO to the engine. Primary regulation of the compressor capacity is made with the 1st stage bypass valve, followed by cylinder valve unloading and if required bypass over stages 2 to 5. With this sequence, the compressor is able to operate flexibly over the full capacity range from 100 to 0 %.

If the amount of nBOG is higher than can be burnt in the engine (for example during early part of the laden voyage) resulting in higher than acceptable suction pressure (tank pressure), the control system will send excess gas to the GCU via the side stream of the 1st  compression stage.

Fig. 15: Simplified flow sheet

In the event of engine shutdown or sudden change in engine load, the compressor delivery line must be protected against overpressure by opening bypass valves over the HP section of the compressor.

During start-up of the compressor with warm nBOG, the temperature control valves will operate to direct a flow through an additional gas intercooler after the 1st compression stage.

The control concept for the compressor is based on one main control mode which is called “power saving mode”. This mode of running, which minimizes the use of gas bypass as the primary method of regulation, operates within various well defi ned control limits.

The system pressure control limits are as follows:

Pmin suction Prevents under-pressure in compressor inlet manifold - tank vacuum.

Phigh suction Suction manifold high pressure - system safety (GCU) on standby.

Pmax suction Initiates action to reduce inlet manifold pressure.

Pmax Prevents overpressure of

ME-GI feed compressor discharge manifold.

A detailed description of operation within these control limits is given below.

Power saving mode

Economical regulation of a multi-stage compressor is most efficiently executed using gas recycle around the 1st stage of compression. The ME-GI required set pressure Pset is therefore taken as control input directly to the compressor

1st stage bypass valve, which will open or close until the actual compressor discharge pressure is equal to the Pset. With this method of control, BOG delivery to the ME-GI is regulated without any direct measurement and control of the delivered mass flow. If none of the above control limits are active, the controller is able to regulate the mass flow in the range from 0 to 100 %.

The following control limits act to overrule the ME-GI controller setting and initiate bypass valve operation:

Pmin suction (tank pressure below set level)

The control scenario is falling suction pressure. If the Pmin limit is active, the 1^st stage recycle valve will not be permitted to close further, thereby preventing further reduction in suction pressure. If the pressure in the suction line continues to decrease, the recycle valve will open governed by the Pmin limiter.

Action of Pressure will fall at the ME-GI control compressor discharge system: requiring the HFO injection rate to be increased.

fBOG: If a spray cooling or forced vaporizer is installed, it may be used for stabilising the suction pressure and thereby increase the gas mass flow to the engine. Such a system could be activated by the Pmin suction pressure limit.

Phigh suction (tank pressure above set level)

The control scenario is increasing suction pressure due to either reduced engine load (e.g. approaching port, manoeuvring) or excess nBOG due to liquid impurities (e.g. N2).

The control limiter initiates a manual start of the GCU (the GCU is assumed not to be on standby mode during normal voyage).

There is no action on the compressor control or the ME-GI control system.

Pmax suction (tank pressure too high)

The control scenario is the same as described above, however, it has resulted in even higher suction pressure. Action must now be taken to reduce suction pressure by sending gas to the GCU.

The high pressure alarm initiates a manual sequence whereby the 1^st stage bypass valve PCV01 is closed and the bypass valve PCV02 to the GCU is opened. When the changeover is completed, automatic Pset control is transferred to the GCU control valve PCV02. The gas amount which cannot

be accepted by the ME-GI will be

Machinery Room Installation – 6LP250-5S

The layout of the cargo handling equipment and the design of their supporting structure presents quite a challenge to the shipbuilder where space on deck is always at a premium. In conjunction with HHI and the compressor maker, an optimised layout of the fuel gas compressor has been developed.

There are many factors which influence the compressor plant layout apart from limited space availability. (See Fig. 16.) External piping connections, adequate access for operation and maintenance, equipment design and manufacturing codes, plant lifting and installation are just a few.

The compressor together with accessory items comprising motor drive, auxiliary oil system, vessels, gas coolers, interconnecting piping, etc., are manufactured as modules requiring minimum assembly work on the ship deck. Separate auxiliary systems provide coolant for the compressor frame and gas coolers.

If required, a dividing bulkhead may separate the main motor drive from the hazardous area in the compressor room. A compact driveshaft arrangement without bulkhead, using a suitably designed ex motor, is however preferred.

Platforms and stairways provide access to the compressor cylinders for valve maintenance. Piston assemblies are withdrawn vertically through manholes in the roof of the machinery house (see Fig. 17).

Requirements for Cargo Machinery Room Support  Structure

Fig. 18 shows details of the compressor base frame footprint and requirement for support by the ship structure.

Reciprocating compressors, by nature of movement of their rotating parts, exhibit out-of-balance forces and moments which must be considered in the design of the supporting structure for acceptable machinery vibration levels.

As a boundary condition, the structure underneath the cargo machinery room must have adequate weight and stiffness to provide a topside vibration level of (approximately) 1.2 - 1.5 mm/s. Satisfactory vibration levels for compressor frame and cylinders are 8 and 15 mm/s respectively (values given are rms – root mean square).

Foundation deflection due to ship movement must, furthermore, be considered in the design of the compressor plant to ensure stress-free piping terminations.

Maintenance requirements - availability/reliability

The low speed, crosshead type compressor design 6LP250-5S, like the ME-GI diesel engine, is designed for the life time of the LNG carrier (25 to 30 years or longer). Routine maintenance is limited purely to periodic checking in the machinery room.

Maintenance intervention for dismantling, checking and eventual part replacement is recommended after

each 8,000 hours of operation. Annual maintenance interventions will normally require 50-70 hours work for checking and possible replacing of wearing parts.

Major intervention for dismantling and bearing inspection is recommended every 2-3 years.

Average availability per compressor unit is estimated to be 98.5 % with best availability approximately 99.5 %. With an installed redundant unit, the compressor plant availability will be in the region of 99.25 %.

Any unscheduled stoppage of the 6LP250-5S compressor will most likely be attributable to a mal-function of a cylinder valve. With the correct valve design and material selection (Burckhardt uses its own design and manufacture plate valves) these events will be very seldom, however a valve failure in operation cannot be entirely ruled out.

LNG boil-off gas is an ideal gas to compress.  The gas is relatively pure and uncontaminated, the gas components are well defined, and the operating temperatures are stable once “cool-down” is completed.

These conditions are excellent for long lifetime of the compressor valves where an average lifetime expectancy for valve plates is 16,000 hours. Therefore, we do not expect any unscheduled intervention

per year for valve maintenance. Such a maintenance intervention will take approx. 7-9 hours for compressor shutdown, isolation and valve replacement.

A total unscheduled maintenance intervention time of 25 hours, assuming 8,000 operating hours per year, may be used for statistical comparison. On this basis compressor reliability is estimated

at 99.7 %.

Our experience in many installations shows that no hours are lost for unscheduled maintenance. The reliability of these compressors is therefore comparable to that of centrifugal compressor types.

Requirements for Classification

            When entering the LNG market with the combined two-stroke and reliquefaction solution, it was discovered that there is a big difference in the requirements from operators and classification societies.

Being used to cooperating with the  classification societies on other commercial ships, the rules and design recommendations for the various applications in the LNG market are new when it comes to diesel engine propulsion. In regard to safety, the high availability  and reliability offered when using the two-stroke engines generally fulfi l the

requirements, but as the delivery and pick up of gas in the terminals is carried out within a very narrow time window, redundancy is therefore essential to the operators.

As such, a two-engine ME-GI solution is the new choice, with its high efficiency, availability and reliability, as the traditional HFO burning engines.

Compared with traditional diesel operated ships, the operators and shipowners in the LNG industry generally have different goals and demands to their LNG tankers, and they often apply  more strict design criteria than applied so far by the classification societies.

A Hazid investigation was therefore  found to be the only way to secure that all situations are taken into account when using gas for propulsion, and that all necessary precautions have been taken to minimize any risk involved.

In 2005, HHI shipyard, HHI engine builder, BCA and MAN Diesel therefore worked out a hazard identifi cation study that was conducted by Det Norske Veritas (DNV), see Appendix V.

Actual Test and Analysis of Safety when Operatingon Gas

The use of gas on a diesel engine calls for careful attention with regard to safety. For this reason, ventilated double walled piping is a minimum requirement to the transportation of gas to the  engine.

In addition to hazard considerations  and calculations, it has been necessary to carry out tests, two of which were carried out some years ago before the installation and operation of the Chiba power plant 12K80MC-GI engine in 1994.

A crack in the double-wall inner pipe

The first test was performed by introducing a crack in the inner pipe to see if the outer pipe would stay intact. The  test showed no penetration of the outer pipe, thus it could be concluded that the double-wall concept lived up to the  expectations.

Pressure fluctuation

The second test was carried out to investigate the pressure fluctuations in the relatively  long piping from the gas compressor to the engine. By estimation of the necessary buffer volume in the piping system, the stroke and injection of gas was calculated to see when safe pressure fluctuations are achieved within given limits for optimal performance of the engines. The piping system has been designed on the basis of these calculations.

Main Engine Room Safety

The latest investigation, which was recently finished, was initiated by a number of players in the LNG market questioning the use of 250 bar gas in the engine room, which is also located under the wheel house where the crew is working and living.

Even though the risk of full breakage happening is considered close to negligible and, in spite of the precautions introduced in the system design, MAN Diesel found it necessary to investigate the effect of such an accident, as the question still remains in part of

the industry: what if a double-wall pipe breaks in two and gas is released from a full opening and is ignited?

As specialists in the offshore industry, DNV were commissioned to simulate such a worst case situation, study the consequences, and point to the appropriate countermeasures. DNV’s work comprised a CFD (computational fluid dynamics)  imulation of the hazard of an explosion and subsequent fire, and an investigation of the risk of this situation ever occurring and at what scale. 

As input for the simulation, the volume of the engine room space, the position of major components, the air ventilation  rate, and the location of the gas pipe and control room were the key input parameters.

Realistic gas leakage scenarios were defined, assuming a full breakage of the outer pipe and a large or small hole in the inner fuel pipe. Actions from the closure of the gas shutdown valves, the ventilation system and the ventilation conditions prior to and after detection are included in the analysis. The amount of gas in the fuel pipe limits the

duration of the leak. Ignition of a leak  causing an explosion or a fire is furthermore factored in, due to possible hotspots or electrical equipment that can give sparks in the engine room.

Calculations of the leak rate as a function of time, and the ventilation flow rates were performed and applied as input to the explosion and fire analyses

Simulation Results

The probability of this hazard happening is based on experience from the offshore industry.

Even calculated in the worst case, no structural damage will occur in the HHI LNG engine room if designed for 1.1bar over pressure.

No areas outside the engine room will be affected by an explosion. If this situation is considered to represent

too high a risk, unattended machinery space during gas operation can be introduced. Today, most engines and equipment are already approved by the classification societies for this type of operation.

By insulation, the switchboard room floor can be protected against heat from any jet fires.

No failure of the fuel oil tank structure, consequently no escalation of fire. The above conclusion is made on the assumption that the GI safety system is fully working. In addition,

DNV has arrived at a different result based on the assumption that the safety system is not working. Onthe basic in these results DNV have put up failure frequencies and developed a set of requirements to be followed in case a higher level of safety is required.

After these conclusion made by DNV,HHI has developed a level for their engine room safety that satisfies the requirements from the classification societies, and also the requirements that are expected from the shipowners.

This new engine room design is based on the experience achieved by HHI with their first orders for LNG carriers equipped with 2 x 6S70ME-C and reliquefaction plant. The extra safety that will be included is listed below:

Double-wall piping is located as far away as possible from critical walls such as the fuel tank walls and switchboard room walls. In case of an engine room fire alarm,  a gas shutdown signal is sent out, the engine room ventilation fans stops, and the air inlet canals are blocked.

During gas running it is not possible to perform any heavy lifting with the engine room crane. A failure of the engine room ventilation will result in a gas shutdown. HC sensors are placed in the engine room, and their position will be based on a dispersion analysis made for the purpose of finding the best location for the sensors.

The double-wall piping is designed with lyres, so that variation in temperatures from pipes to surroundings can be absorbed in the piping. In fact, any level of safety can be

achieved on request of the shipowner  The safety level request will be achieved in a co-operation between the yard HHI, the engine builder HHI, the classification society and MAN Diesel A/S.

The report “Dual fuel Concept: Analysis of fires and explosions in engine room” was made by DNV consulting and can be ordered by contacting MAN Diesel A/S, in Copenhagen.

Engine Operating Modes

One of the advantages of the ME-GI engine is its fuel flexibility, from which an LNG carrier can certainly benefi t. Burning the boil-off gas with a variation in the heat value is perfect for the diesel working principle. At the start of a laden voyage, the natural boil-off gas holds a large amount of nitrogen and

the heat value is low. If the boil-off gas is being forced, it can consist of both ethane and propane, and the heat value could be high. A two-stroke, high-pressure gas injection engine is able to burn those different fuels and also without a drop in the thermal effi ciency of the engine. The control concept comprises

two different fuel modes, see also Fig. 19.  fuel-oil-only mode minimum-fuel mode

The fuel-oil-only mode is well known from the ME engine. Operating the engine in this mode can only be done on fuel oil. In this mode, the engine is considered “gas safe”. If a failure in the gas system occurs it will result in a gas shutdown and a return to the fuel-oilonly mode and the engine is “gas safe”.

The minimum-fuel mode is developed for gas operation, and it can only be started manually by an operator on the  Gas Main Operating Panel in the control room. In this mode, the control system

will allow any ratio between fuel oil and gas fuel, with a minimum preset amount of fuel oil to be used.

The preset minimum amount of fuel oil, hereafter named pilot oil, to be used is in between 5-8% depending on the fuel oil quality. Both heavy fuel oil and marine diesel oil can be used as pilot oil. The min. pilot oil percentage is calculated from 100% engine load, and is constant in the load range from 30-

100%. Below 30% load MAN Diesel is not able to guarantee a stable gas and pilot oil combustion, when the engine reach this lower limit the engine returns to Fuel-oil-only mode.

Gas fuels correspond to low-sulphur fuels, and for this type of fuel we recommend the cylinder lube oil TBN40 to be used. Very good cylinder condition with this lube oil was achieved from the gas engine on the Chiba power plant.

A heavy fuel oil with a high sulphur content requires the cylinder lube oil TBN 70. Shipowners intending to run their engine on high-sulphur fuels for longer periods of time are recommended to install two lube oil tanks. When changing to minimum-fuel mode, the change of lube oil should be carried out as well.

Players in the market have been focused on reducing the exhaust emissions during harbour manoeuvring. When testing the ME-GI at the MAN Diesel research centre in Copenhagen, the 30% limit for minimum-fuel mode will be challenged taking advantage of the increased possibilities of the ME fuel

valves system to change its injection profi le, MAN Diesel expects to lower this 30% load limit for gas use, but for now no guaranties can be given.

Fig. 19: Fuel type modes for the ME-GI engines for LNG carriers

Launching the ME-GI

As a licensor, MAN Diesel expects a time frame of two years from order to delivery of the first ME-GI on  the test bed.

In the course of this time, depending on the ME-GI engine size chosen, the engine builder will make the detailed designs and a final commissioning test on a research engine. This type approval test (TAT) is to be presented to the classification society and ship owner in question to show that the compressor and the ME-GI engine is working in all the operation modes and conditions.

In cooperation with the classification society and engine builder, the most optimum solution, i.e. to test the  compressor and ME-GI engine before delivery to the operator has been considered and discussed. One  solution is  to test the gas engine on the test bed, but this is a costly method. Alternatively, and recommended by MAN Diesel, the compressor and ME-GI operation test could be made in continuation  of the gas trial. Today, there are different opinions among the classification societies, and both solutions are possible depending on the choice of classification society and arrangement between ship owners, yard and engine builder.

MAN Diesel A/S has developed a test philosophy especially for approval of the ME-GI application to LNG carriers, this philosophy has so far been approved by DNV, GL, LR and ABS, see Table III. The idea is that the FAT (Factory Acceptance Test) is being performed for  the ME system like normal, and for the GI system it is performed on board the

LNG carrier as a part of the Gas Trial Test. Thereby, the GI system is tested in combination with the tailor-madegas compressor system for the specific LNG carrier. Only in this combination it will be possible to get a valid test.

Prior to the gas trial test, the GI system has been tested to ensure that everything

is working satisfactory

CHAPTER-10

ME-GI Engines for LNG Application

System Control and Safety

For these plants, the boil-off gas is returned to the LNG tanks in liquefied form via

a reliquefaction plant installed on board.

Some operators are considering an alternative two-stroke solution, which is the

ME-GI (Gas Injection) engine operating at a 250-300 bar gas pressure.

Which solution is optimal for a given project depends primarily on the price of HFO and the value of natural gas.

Calculations carried out by MBD sow that additional USD 3 million can be secured as profit per year when using two-stroke diesel engines, irrespective of whether the HFO or the dual fuel engine type is chosen. When it comes to first cost, the HFO diesel engine combined with a reliquefaction plant has the same cost level as the steam turbine solution, whereas the dual fuel ME-GI engine with a compressor is a cheaper solution.

This paper will describe the application of ME-GI engines inclusive the gas supply system on a LNG carriers, and the layout and control system for both the

engine and gas supply system.

First, a short description is given of the propulsion power requirement of LNG

carriers, and why the two-stroke diesel engine is winning in this market.

Propulsion power requirements for LNG carriers

Traditionally, LNG carriers have been sized to carry 130,000 – 140,000 m3 liquefied natural gas, i.e. with a carrying capacity of some 70-80,000 tons, which resembles that of a panamax bulk carrier.

The speed has been around 20 knots, whereas that of the panamax bulk carriers is around 15. Now, even larger LNG carriers are in project up to a capacity of some 250,000 m3 LNG. Such ships will be comparable in size to a capsize bulk carrier and an aframax tanker but, again, with a speed higher than these.

In an analysis of the resulting power requirements, a calculation programme normally used by MBD has been used, Ref. [2].

The result appears in Fig. 1, which shows that a power requirement of 30 to 50 MW is needed.

Fig. 1: Typical propulsion power requirements for LNG carriers

Fig. 2: Typical thermal efficiencies of prime movers

As mentioned, diesels are now being seen as an alternative to steam, first of all because of the significant difference in thermal efficiency reflected also in the system efficiency, as illustrated in Fig. 2.

With a power requirement of the mentioned magnitude, the illustrated efficiency difference of up to 20 percentage points   amounts to significant savings both in terms of energy costs and in terms of emissions.

The desired power for propulsion can be generated by a single, double, or multiple fuel or gas driven diesel engine installation with either direct geared or diesel-electric drive of one or two propellers. The choice depends on economical and operational factors. Over time, the evaluation of these factors for the options of propulsion technology, for ordinary larger cargo vessels (viz. container vessels, bulk carriers and tankers), has led to the selection of a single, heavy-fuel-burning, low speed diesel engine in more than 90% of contemporary vessels.

The aim of this paper is to demonstrate that low speed propulsion is fully feasible for LNG carriers.

Boil-off Gas from LNG Cargo

The reason for having a continuous evaporated rate of boil-off gas is that it is generated by heat transferred from the ambient temperature through the LNG tanks and into to cold LNG. The boil-off gas is the consequence if the LNG cargo should be staying liquid at atmospheric pressure and at a temperature of some minus 160 degrees Celsius. To keep the evaporated rate of boil-off at a minimised level, the cargo is kept in proper insulated tanks.

The LNG is a mixture of methane, ethane and nitrogen. Other natural gases like butane and propane are extracted during the liquefying and are only present in very small quantities.

 In a traditional steam turbine vessel, the boil-off gas is conveniently sent to twin boilers to produce steam for the propulsion turbine. Due to the proper insulation, the boil-off is usually not enough to provide the energy needed for propulsion, so the evaporated gas is supplemented by either forced boil off of gas or heavy fuel oil to produce the required steam amount.

In a diesel engine driven LNG carrier, the energy requirement is less thanks to the higher thermal efficiency, so the supplementary energy by forced boil off or heavy fuel oil can be reduced significantly, as shown in Fig. 3

Fig. 3: Propulsion alternative – energy need for propulsion

Fig. 4: Fuel Type Modes – MAN B&W two-stroke dual fuel low speed diesel

Design of the Dual Fuel ME-GI Engine

In terms of engine performance (i.e.: output, speed, thermal efficiency, exhaust gas amount and temperature, etc.) the ME-GI engine series is generally identical to the well-established and type approved ME engine series. This means that the application potential for the ME-engine series applies to the ME-GI engine series as well – provided that gas is available as a main fuel. All ME engines can be offered as ME-GI engines.

Consequently, the following description of the ME-GI engine design only deals with new or modified engine components with the different fuel mode types, as illustrated in Fig. 4.The control system will allow any ratio between fuel and gas, with a preset minimum fuel amount to be used.

Fig.6: General arrangement of double-wall piping system for gas

General Description

Fig. 5 shows the cross-section of a S70ME-GI, with the new modified parts of the ME-GI engine pointed out, comprising gas supply piping, large-volume accumulator on the (slightly modified) cylinder cover with gas injection valves, and HCU with ELGI valve for control of the injected gas amount. Further to this, there are small modifications to the exhaust gas receiver, and the control  and manoeuvring system.

Apart from these systems on the engine, the engine auxiliaries will comprise some new units, the most important ones being:

Fig. 5: New modified parts on the ME-GI engine

• High-pressure gas compressor supply system, including a cooler, to raise the pressure to 250-300 bar, which is the pressure required at the engine inlet.

• Pulsation/buffer tank including a condensate separator.

• Compressor control system.

• Safety systems, which ex. includes a hydrocarbon analyser for checking the hydro-carbon content of the air in the compressor room and in the double-wall gas pipes.

• Ventilation system, which ventilates the outer pipe of the double-wall piping completely.

• Sealing oil system, delivering sealing oil to the gas valves separating the control oil and the gas.

• Inert gas system, which enables purging of the gas system on the engine with inert gas.

Fig. 6, in schematic form, shows the system layout of the engine. The high pressure gas from the compressor-unit flows through the main pipe via narrow and flexible branch pipes to each  cylinder’s gas valve block and large-volume accumulator.  The narrow and flexible branch pipes perform two important tasks:

• They separate each cylinder unit from the rest in terms of gas dynamics, utilizing the well- proven design philosophy of the ME engine’s fuel oil system.

• They act as flexible connections between the stiff main pipe system and the engine structure, safeguarding against extra-stresses in the main and branch pipes caused by the inevitable differences in thermal expansion of the gas pipe system and the engine structure.

Fig. 7: ME-GI fuel injection system

The large-volume accumulator, containing about 20 times the injection amount per stroke at MCR, also performs two important tasks:

• It supplies the gas amount for injection at only a slight, but predetermined, pressure drop.

• It forms an important part of the safety system (as described later).

Since the gas supply system is a common rail system, the gas injection valve must be controlled by another system, i.e. the control oil system. This, in principle, consists of the ME hydraulic control (servo) oil system and an ELGI valve, supplying high-pressure control oil to the gas injection valve, thereby control-ling the timing and opening of the gas valve.

As can also be seen in Fig. 7, the normal fuel oil pressure booster, which supplies pilot oil in the dual fuel operation mode, is connected to the ELGI valve by a pressure gauge and an on/ off valve incorporated in the ELGI valve.

By the control system, the engine can be operated in the various relevant modes: normal “dual-fuel mode” with minimum pilot oil amount, “specified gas mode” with injection of a fixed gas amount, and the “fuel-oil-only mode”.

The ME-GI control and safety system is built as an add-on system to the ME control and safety system. It hardly requires any changes to the ME system, and it is consequently very simple to implement.

The principle of the gas mode control system is that it is controlled by the error between the wanted discharge pressure and the actual measured discharge pressure from the compressor

system. Depending on the size of this error the amount of fuel-gas (or of pilot oil) is either increased or decreased.

If there is any variation over time in the calorific value of the fuel-gas it can be measured on the rpm of the crankshaft. Depending on the value measured, the amount of fuel-gas is either increased or decreased.

The change in the calorific value over time is slow in relation to the rpm of the engine. Therefore the required change of gas amount between injections is relatively small.

To make the engine easy to integrate with different suppliers of external gas delivering systems, the fuel gas control system is made almost “stand alone”. The exchanged signals are limited to top, Go, ESD, and pressure set-point signals.

Fig. 8: Engine control system diagram

System description

Compared with a standard engine for heavy fuel operation, the adaptation to high-pressure gas injection requires that the design of the engine and the pertaining external systems will comprise a number of special external components and changes on the engine.

Fig. 9 shows the principal layout of the gas system on the engine and some of the external systems needed for dual fuel operation.In general, all systems and components described in the following are to be made “fail safe”,  meaning that components and systems will react to the safe side if anything goes wrong.

Fig. 9: Internal and external systems for dual fuel operation

Engine systems

In the following, the changes of the systems/ components on the engine, as pointed out in Fig. 5, will be described.

Exhaust receiver

The exhaust gas receiver is designed to withstand the pressure in the event of ignition failure of one cylinder followed by ignition of the unburned gas in the receiver (around 15 bars).

The receiver is furthermore designed with special transverse stays to withstand such gas explosions.

Fuel injection valves

Dual fuel operation requires valves for both the injection of pilot fuel and gas fuel.

The valves are of separate types, and two are fitted for gas injection and two for pilot fuel. The media required for both fuel and gas operation is shown below:

• High-pressure gas supply

• Fuel oil supply (pilot oil)

• Control oil supply for activation

of gas injection valves

• Sealing oil supply.

The gas injection valve design is shown in Fig. 10.

Fig. 10: Gas injection valve

This valve complies with our traditional design principles of compact design and the use of mainly rotational symmetrical parts. The design is based on the principle used for an early version of a combined fuel oil/gas injection valve as well as experience gained with our normal fuel valves.

Gas is admitted to the gas injection valve through bores in the cylinder cover. To prevent gas leakage between cylinder cover/gas injection valve and valve housing/spindle guide, sealing rings made of temperature and gas resistant material are installed. Any gas leakage through the gas sealing rings will be led through bores in the gas injection valve and the cylinder cover to the double-wall gas piping system, where any such leakages will be detected by HC sensors.

The gas acts continuously on the valve spindle at a pressure of about 250-300 bar. In order to prevent the gas from entering the control oil activating system via the clearance around the spindle, the spindle is sealed by means of sealing oil led to the spindle clearance at a pressure higher than the gas pressure (25-50 bar higher).

The pilot valve is a standard fuel valve without any changes.

Both designs of gas injection valves will allow operation solely on fuel oil up to MCR. lf the customer’s demand is for the gas engine to run at any time at 100 % load on fuel oil, without stopping the engine for changing the injection equipment, the fuel valve nozzle holes will be as the standard type for normal fuel oil operation. In this case, it may be necessary to use a somewhat larger amount of pilot fuel in order to assure a good injection quality and safe ignition of the gas.

Cylinder cover

In order to protect the gas injection nozzle and the pilot oil nozzle against tip burning, the cylinder cover is designed with a welded-on protective guard in front of the nozzles.

The side of the cylinder cover facing the HCU (Hydraulic Cylinder Unit) block has a face for the mounting of a special valve block, see later description.

In addition, the cylinder cover is provided with two sets of bores, one set for supplying gas from the valve block to each gas injection valve, and one set for leading any leakage of gas to the sub-atmo-Fig. 9: Internal and external systems for dual fuel operation spheric pressure, ventilated part of the double-wall piping system.

Hydraulic Cylinder Unit (HCU)

To reduce the number of additional hydraulic pipes and connections, the ELGI valve as well as the control oil pipe connections to the gas valves will be incorporated in the design of the HCU.

Valve block

The valve block consists of a square steel block, bolted to the HCU side of the cylinder cover.

The valve block incorporates a large volume accumulator, and is provided with a shutdown valve and two purge valves on the top of the block. All highpressure gas sealings lead into spaces that are connected to the double-wall pipe system, for leakage detection.

The gas is supplied to the accumulator via a non-return valve placed in the accumulator inlet cover.

To ensure that the rate of gas flow does not drop too much during the injection period, the relative pressure drop in the accumulator is measured. The pressure drop should not exceed about 20-30 bar.

Any larger pressure drop would indicate a severe leakage in the gas injection valve seats or a fractured gas pipe. The safety system will detect this and shut down the gas injection.

From the accumulator, the gas passes through a bore in the valve block to the shut down valve, which in the gas mode, is kept open by compressed air. From the shutdown valve (V4 in Fig. 9), the gas is led to the gas injection valve via bores in the valve block and in the cylinder cover.

A blow-off valve (V3 in Fig. 9), placed on top of the valve block, is designed to empty the gas bores when needed.

A purge valve (V5 shown in Fig. 9), which is also placed on top of the valve block, is designed to empty the accumulator when the engine is no longer to operate in the gas mode.

Gas pipes

A common rail (constant pressure) system is to be fitted for high-pressure gas distribution to each valve block.

Gas pipes are designed with double walls, with the outer shielding pipe designed so as to prevent gas outflow to the machinery spaces in the event of rupture of the inner gas pipe. The intervening space, including also the space around valves, flanges, etc., is equipped with separate  mechanical ventilation with a capacity of approx. 10 – 30 air changes per hour. The pressure in the  intervening space is to be below that of the engine room and, as mentioned earlier, (extractor) fan motors are to be placed outside the ventilation ducts, and the fan material must be manufactured from spark-free material. The ventilation inlet air must be taken from a gas safe area.

Gas pipes are arranged in such a way, see Fig. 6, that air is sucked into the double-wall piping system from around the pipe inlet, from there into the branch pipes to the individual cylinder blocks, via the branch supply pipes to the main supply pipe, and via the suction blower to the atmosphere. Ventilation air is to be exhausted to a safe place.

The double-wall piping system is designed so that every part is ventilated. however, minute volumes around the gas injection valves in the cylinder cover are not ventilated by flowing air for practical reasons. Small gas amounts, which in case of leakages may accumulate in these small clearances, blind ends, etc. cannot be avoided, but the amount of gas will be negligible. Any other leakage gas will be led to the ventilated part of the double-wall piping system and be detected by the HC sensors.

The gas pipes on the engine are designed for 50 % higher pressure than the normal working pressure, and are supported so as to avoid mechanical vibrations.

The gas pipes should furthermore be protected against drops of heavy items. The pipes will be pressure tested at 1.5 times the working pressure. The design is to be all-welded as far as practicable, with flange connections only to the necessary extent for servicing purposes.

The branch piping to the individual cylinders must be flexible enough to cope with the thermal expansion of the engine from cold to hot condition.

The gas pipe system is also to be designed so as to avoid excessive gas pressure fluctuations during operation. Finally, the gas pipes are to be connected to an inert gas purging system.

Fuel oil booster system

Dual fuel operation requires a fuel oil pressure booster, a position sensor, a FIVA valve to control the injection of pilot oil, and an ELGI valve to control the injection of gas. Fig. 7 shows the design control principle with the two fuel valves and two gas valves.

No change is made to the ME fuel oil pressure booster, except that a pressure sensor is added for checking the pilot oil injection pressure. The injected amount of pilot oil is monitored by the position sensor.

The injected gas amount is controlled by the duration of control oil delivery from the ELGI valve. The operating medium is the same servo oil as is used for the fuel oil pressure booster.

Miscellaneous

Other engine modifications will, basically, be limited to a changed position of pipes, platform cut-outs, drains, etc.

Safety aspects

The normal safety systems incorporated in the fuel oil systems are fully retained also during dual fuel operation. However, additional safety devices will be incorporated in order to prevent situations which might otherwise lead to failures.

Safety devices – External systems

Leaky valves and fractured pipes are sources of faults that may be harmful. Such faults can be easily and quickly detected by a hydro-carbon (HC) analyzer with an alarm function. An alarm is given at a gas concentration of max. 30% of the Lower Explosion Limit (LEL) in the vented duct, and a shut down signal is given at 60% of the LEL.

The safety devices that will virtually eliminate such risks are double-wall pipes and encapsulated valves with ventilation of the intervening space. The ventilation between the outer and inner walls is always to be in operation when there is gas in the supply line, and any gas leakage will be led to the HC-sensors placed in the outer pipe.

Another source of fault could be a malfunctioning sealing oil supply system. If the sealing oil  pressure becomes too low in the gas injection valve, gas will flow into the control oil activation system and, thereby, create gas pockets and prevent the ELGI valve from operating the gas injection valve. Therefore, the sealing oil pressure is measured by a set of pressure sensors, and in the event of a too low pressure, the engine will shut down the gas mode and start running in the fuel oil mode.

Lack of ventilation in the double-wall piping system prevents the safety function of the HC  sensors, so the system is to be equipped with a set of flow switches. If the switches indicate no flow, or nearly no flow, an alarm is given. If no correction is carried out, the engine will be shut down on gas mode. The switches should be of the normally open (NO) type, in order to allow detection of a malfunctioning switch, even in case of an electric power failure.

• In case of malfunctioning valves (not leaky) resulting in insufficient gas supply to the engine, the gas pressure will be too low for gas operation. This is dealt with by monitoring the pressure in the accumulator in the valve block on each cylinder. The pressure could be monitored by either one pressure pick-up, or by a pressure switch and a differential pressure switch (see later for explanation).

As natural gas is lighter than air, non-return valves are incorporated in the gas system’s outlet pipes to ensure that the gas system is not polluted, i.e. mixed with air, thus eliminating the potential risk of explosion in case of a sudden pressure increase in the system due to quick opening of the main gas valve.

For LNG carriers in case of too low a BOG pressure in the LNG tanks, a stop/off signal is sent to the ME-GI control system and the gas mode is stopped, while the engine continues running on HFO.

Safety devices – Internal systems

During normal operation, a malfunction in the pilot fuel injection system or gas injection system may involve a risk of uncontrolled combustion in the engine.

Sources of faults are:

• Defective gas injection valves

• Failing ignition of injected gas

These aspects will be discussed in detail in the following together with the suitable counter measures.

Defective gas injection valves

In case of sluggish operation or even seizure of the gas valve spindle in the open position, larger gas quantities may be injected into the cylinder, and when the exhaust valve opens, a hot mixture of combustion products and gas flows out and into the exhaust pipe and further on to the exhaust receiver. The temperature of the mixture after the valve will increase considerably, and it is likely that the gas will burn with a diffusion type flame (without exploding) immediately after the valve where it is mixed with scavenge air/exhaust gas (with approx. 15 per cent oxygen) in the exhaust system. This will set off the high exhaust gas temperature alarm for the cylinder in question. In the unlikely event of larger gas amounts entering the exhaust receiver without starting to burn immediately, a later ignition may result in violent burning and a corresponding pressure rise. Therefore, the exhaust receiver is designed for the maximum pressure (around 15 bars).

However, any of the above-mentioned situations will be prevented by the detection of defective gas valves, which are arranged as follows:

The gas flow to each cylinder during one cycle will be detected by measuring the pressure drop in the accumulator. This is to ensure that the injected gas amount does not exceed the amount corresponding to the MCR value.

It is necessary to ensure that the pressure in the accumulator is sufficient for gas operation, so the accumulator will be equipped with a pressure switch and a differential pressure switch. An increase of the gas flow to the cylinder which is greater than corresponding to the actual load, but smaller than corresponding to the MCR value, will only give rise to the above-mentioned exhaust gas temperature alarm, and is not harmful.

By this system, any abnormal gas flow, whether due to seized gas injection valves or fractured gas pipes, will be detected immediately, and the gas supply will be discontinued and the gas lines purged with inert gas.

In the case of slightly leaking gas valves, the amount of gas injected into the cylinder concerned will increase. This will be detected when the exhaust gas temperature increases. Burning in the exhaust receiver will not occur in this situation due to the lean mixture.

Ignition failure of injected gas

Failing ignition of the injected natural gas can have a number of different causes, most of which, however, are the result of failure to inject pilot oil in a cylinder:

• Leaky joints or fractured high-pressure pipes, making the fuel oil booster inoperative.

• Seized plunger in the fuel oil booster.

• Other faults on the engine, forcing the

fuel oil booster to “O-index”.

• Failing pilot oil supply to the engine.

Any such faults will be detected so quickly that the gas injection is stopped immediately from the first failure to inject the pilot oil.

In extremely rare cases, pilot fuel can be injected without being ignited, namely in the case of a sticking or severely burned exhaust valve. This may involve such large leakages that the compression pressure will not be sufficient to ensure ignition of the pilot oil. Consequently, gas and pilot fuel from that cylinder will be supplied to the exhaust gas receiver in a fully unburned condition, which might result in violent burning in the receiver. However, burning of an exhaust valve is a rather slow process extending over a long period, during which the exhaust gas temperature rises and gives an alarm well in advance of any situation leading to risk of misfiring.

A seized spindle in the pilot oil valve is another very rare fault, which might influence the safety of the engine in dual fuel operation. However, the still operating valve will inject pilot oil, which will ignite the corresponding gas injection, and also the gas injected by the other gas valve, but knocking cannot be ruled out in this case. The cylinder pressure monitoring system will detect this condition.

As will appear from the above discussion, which has included a number of very unlikely faults, it is possible to safeguard the engine installation and personnel and, when taking the proper countermeasures, a most satisfactory service reliability and safety margin is obtained.

External systems

The detailed design of the external systems will normally be carried out by the individual shipyard/contractor, and is, therefore, not subject to the type approval of the engine. The external systems de- scribed here include the sealing oil system, the ventilation system, and the gas supply and compressor system.

Sealing oil system

The sealing oil system supplies oil, via a piping system with protecting hoses, to the gas injection valves, thereby providing a sealing between the gas and the control oil, and lubrication of the moving parts.

The sealing oil pump has a separate drive and is started before commencing gas operation of the engine. It uses the 200 bar servo oil, or one bar fuel oil, and pres- surises it additionally to the operating pressure, which is 25-50 bar higher than the gas pressure. The consumption is small, corresponding to a sealing oil consumption of approx. 0.1 g/bhph.

After use, the sealing oil is burned in the engine.

Fig. 11: Gas system branching

Ventilation system

The purpose of the ventilation system is to ensure that the outer pipe of the double-wall gas pipe system is ventilated with air, and it acts as a separation between the engine room and the high-pressure gas system, see Fig 11. Ventilation is achieved by means of an electrically driven mechanical fan or extractor fan. If an electrically driven fan is chosen, the motor must be placed outside the ventilation duct. The capacity must ensure approx. 10 – 30 air changes per hour. More ventilation gives quicker detection of any gas leakage. Fig. 12: Gas supply system – natural BOG only

The gas Compressor System

The gas supply system is based on Flotech™ packaged compressors:

§  Low-pressure GE Oil & Gas RoFlo™ type gas compressors with lubricated vanes and oil buffered mechanical seals, which compress the cold boil-off gas from the LNG tanks at the temperature of -140oC to -160oC. The boil-off gas pressure in the LNG tanks should normally be kept between 1.06-1.20 bar(a). Under normal running conditions, cooling is not necessary, but during start up, the temperature of the boil-off gas may have risen to atmospheric temperature, hence pre-heating and after-cooling is included, to ensure stabilisation of the cold inlet and intermediate gas. temperature

§  The high-pressure GE Oil & Gas Nuovo Pignone™ SHMB type gas compressor; 4 throw, 4-stage horizontally opposed and fully balanced crosshead type with pressure lubricated and water-cooled cylinders & packings, compresses the gas to approximately 250-300 bar, which is the pressure required at the engine inlet at full load. Only reciprocating piston compressors are suitable for this high pressure duty; however the unique GE fully balanced frame layout addresses concerns about transmitted vibrations and also eliminates the need for heavy installation structure, as is required with vertical or V-form unbalanced compressor designs. The discharge temperature is kept at approx. 45oC by the coolers.

§  Buffer tank/accumulators are installed to provide smoothing of minor gas pressure fluctuations in the fuel supply; ± 2 bar is required.

§  Gas inlet filter/separator with strainer for protection against debris.

§  Discharge separator after the final stage gas cooler for oil/condensate removal.

§  Compressor capacity control system ensures that the required gas pressure is in accordance with the engine load, and that the boil-off gas amount is regulated for cargo tank pressure control (as described later).

§  The compressor safety system handles normal start/stop, shutdown and emergency shutdown commands. The compressor unit includes a process monitoring and fault indication system. The compressor control system exchanges signals with the MEGI control system.

§  The compressor system evaluates the amount of available BOG and reports to the ME-GI control system.

Fig. 13: Gas supply system– natural and forced BOG

Redundancy for the gas supply system is a very important issue. Redundancy in an extreme sense means two of all components, but the costs are heavy and a lot of space is required on board the ship. We have worked out a recommendation that reduces the costs and the requirement for space while ensuring a fully operational ME-GI engine. The dual fuel engine concept, in its nature, includes redunancy. If the gas supply system falls out, the engine will run on heavy fuel oil only.

The gas supply system illustrated in Fig. 12 and 13 are based on a 210,000 M3 LNG carrier, a boil off rate of 0.12 and equipped with 2 dual fuel engines: 2 x 7S65ME-GI. For other sizes of LNG carriers the setup will be the same but the % will be changed. Figs. 12 and 13 show our recommendations for a gas supply system to be used on LNG carriers, and figure 15 shows the compressor system in more detail. Depending on whether the ship owner wishes to run on natural BOG only, Fig. 12, or run on both natural BOG and forced BOG, Fig. 13 is relevant.

Both systems comprise a double (2 x 100%) set of Low Pressure compressors each with the capacity to handle 100% of the natural BOG if one falls out (alternatively 3 x 50% may be chosen). Each of these LP compressors can individually feed both the High Pressure Compressor and the Gas Combustion Unit. All compressors can run simultaneously, which can be utilised when the engine is fed with both natural - and forced BOG.

The HP compressor section is chosen to be a single unit. If this unit falls out then the ME-GI engine can run on Heavy Fuel Oil, and one of the LP compressors can feed the GCU.

Typical availability of these electrically driven Flotech / GE Oil & Gas compressors on natural gas (LNG) service is 98%, consequently, an extra HP compressor is a high cost to add for the 2% extra availability.

Gas supply system –capacity management

The minimum requirement for the regulation of supply to the ME-GI engine is a turndown ratio of 3.33 which equals a regulation down to 30% of the maximum flow (For a twin engine system, the TR is 6.66). Alternatively in accordance with the requirements of the ship owners

Both the LP and HP compressor packages have 0 => 100% capacity variation systems, which allows enormous flexibility and control.

Stable control of cargo tank pressure is the primary function of the LP compressor control system. Dynamic capacity variation is achieved by a combination of compressor speed variation and gas

Fig. 14: Typical HP fuel oil gas compressor

Fig. 16: Gas compressor system – indicating capacity control & cooling system

discharge to recycle. The system is responsible for maintaining the BOG pressure set tank pressure point within the range of 1,06 – 1,20 bar(a) through 0 100% compressor capacity.

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At full load of the ME-GI engine on gas, the HP compressor delivers approximately 265 bar whereas at 50% load, the pressure is reduced to 130-180 bar. The discharge pressure set points are controlled within ±5%. Compressor speed variation controls the capacity range of approximately 100 => 50% of volumetric flow. Speed control is the primary variation; speed control logic is integrated with recycle to reduce speed/ capacity when the system is recycling

under standby (0% capacity) or part load conditions.

LP & HP compressor systems are coordinated such that BOG pressure is safely controlled, whilst however delivering all available gas at the correct pressure to the ME-GI engine. Load and availability signals are exchanged between compressor and engine control systems for this purpose.

Safety aspects

The compressors are delivered generally in accordance with the API-11P standard (skid-packaged compressors) and are designed and certified in accordance with relevant classification society rules.

Maintenance

The gas compressor system needs an annual overhaul. The overhaul can be performed by the same engineers who do the maintenance on the main engines. It requires no special skills apart from what is common knowledge for an engineer.

External systems

External safety systems should include a gas analyser for checking the hydrocarbon content of the air, inside the compressor room and fire warning and protection systems.

Safety devices – Internal systems

The compressors are protected by a series of Pressure High, Pressure Low, Temperature High, Vibration High, Liquid Level High/Low,

Compressor RPM High/Low and Oil Low Flow trips, which will automatically shut down the compressor if fault conditions are detected by the local control system.

Pressure safety valves vented to a safe area guard against uncontrolled overpressure of the fuel gas supply system.

Inert gas system

After running in the gas mode, the gas system on the engine should be emptied of gas by purging the gas system with inert gas (N2, CO2),

Dual Fuel Control System

General

In addition to the above a special dual fuel control system is being developed to control the dual-fuel operation when the engine is operating on compressed gaseous fuels. See fig. 17. The control system is the glue that ties all the dual fuel parts in the internal and the external system together and makes the engine run in gas mode.

As mentioned earlier the system is designed as an add-on system to the original ME control system. The consequence is that the Bridge panel, the Main Operating Panel (MOP) & the Local Operating Panel (LOP) will stay unchanged. All operations in gas mode are therefore performed from the engine room alone.

When the dual fuel control system is running the existing ME control and alarm system will stay in full operation.

Mainly for hardware reasons the control of the dual fuel operation is divided into:

• Plant control

• Fuel control

• Safety Control

Plant control

The task of the plant control is to handle the switch between the two stable states:

• Gas Safe Condition State ( HFO only)

• Dual-Fuel State

The plant control can operate all the fuel gas equipment shown in fig. 10. For the plant control to operate it is required that the Safety Control allows it to work otherwise the Safety Control will overrule and return to a Gas Safe Condition.

Fuel control

The task of the fuel control is to determine the fuel gas index and the pilot oil index when running in the three different modes shown in fig.4.

Safety control

The task of the safety system is to monitor:

• All fuel gas equipment and the related auxiliary equipment

• The existing shut down signal from the ME safety system.

• The cylinder condition for being in a condition allowing fuel gas to be injected.

If one of the above mentioned failures is detected then the Safety Control releases the fuel gas Shut Down sequence below:

The Shut down valve V4 and the master valve V1 will be closed. The ELGI valves will be disabled. The fuel gas will be blow out by opening valve V2 and finally the gas pipe system will be purged with inert gas. See also fig. 9

Architecture of the Dual Fuel Control System

Dual Fuel running is not essential for the manoeuvrability of the ship as the engine will continue to run on fuel oil if an unintended fuel gas stop occurs. The two fundamental architectural and design demands of the fuel gas Equipment are, in order of priority:

• Safety to personnel must be at least on the same level as for a conventional diesel engine

• A fault in the Dual Fuel equipment must cause stop of gas operation and change over to Gas Safe Condition. Which to some extent complement each other.

The Dual Fuel Control System is designed to “fail to safe condition”. See Fig. 18. All failures detected during fuel gas running and failures of the control system itself will result in a fuel gas Stop / Shut Down and change over to fuel operation.  Followed by blow out and purging of high pressure fuel gas pipes which releases all gas from the entire gas supply system.

If the failure relates to the purging system it may be necessary to carry out purging manually before an engine repair is carried out. (This will be explained later).

The Dual Fuel Control system is a single system without manual back-up control. However, the following equipment is made redundant to secure that a single fault will not cause fuel gas stop:

• The communication network is doubled in order to minimize the risk of interrupting the   communication between the control units.

• Vital sensors are doubled and one set of these sensors is connected to the Plant Control and the other to the Safety System. Consequently a sensor failure which is not detectable is of no consequence for safe fuel gas operation.

Control Unit Hardware

For the Dual Fuel Control System two different types of hardware are used:  the Multi Purpose Controller Units and the GCSU , both developed by MAN B&W Diesel A/S.

The Multi Purpose Controller Units are used for the following units: GECU, GACU, GCCU, and the GSSU see also fig. 17. In the following a functionality description for each units shown in fig. 17

Fig. 17: ME-GI Control System

Gas Main Operating Panel (GMOP)

For the GI control system an extra panel called GMOP is introduced. From here all manually operations can be initiated. For example the change between the different running modes can be done and the operator has the possibility to manually initiate the purging of the gas pipes system with inert gas.

Additionally it contains the facilities to manually start up or to stop on fuel gas.

GECU, Plants control

The GECU handles the Plant Control and in combination with GCCU it also handles Fuel Control.

Example: When “dual fuel” Start is initiated manually by the operator, the Plant

Control will start the automatic start sequence which will initiate start-up of the sealing oil pump. When the engine condition for Dual Fuel running, which is monitored by the GECU, is confirmed

to meet the prescribed demands, the Plant Control releases a “Start Dual Fuel Operation” signal for the GCCU (Fuel Control).

In combination with the GCCU, the GECU will effect the fuel gas injection if all conditions for Dual Fuel running are fulfilled.

The Plant Control monitors the condition of the following:

• HC “Sensors”

• Gas Supply System

• Sealing Oil System

• Pipe Ventilation

• Inert Gas System

• Network connection to other units of

the Dual Fuel System

and, if a failure occur, the Plant Control will automatically interrupt fuel gas start  operation and return the plant to Gas Safe Condition.

The GECU also contains the Fuel Control which includes all facilities required for calculating the fuel gas index and the Pilot Oil index based on the command from the conventional governor and the actual active mode.

Based on these data and including information about the fuel gas pressure, the Fuel Control calculates the start and duration time of the injection, then sends the signal to GCCU which effectuates the injection by controlling the ELGI valve.

GACU, Auxiliary Control

The GACU contains facilities necessary to control the following auxiliary systems: The fan for ventilating of the double wall pipes, the sealing oil pump, the purging with inert gas and the gas supply system.

The GACU controls:

• Start/stop of pumps, fans, and of the gas supply system.

• The sealing oil pressure set points

• The pressure set points for the gas supply system.

GCCU, ELGI control

The GCCU controls the ELGI valve on the basics of data calculated by the GECU.

In due time before each injection the GCU receives information from the GECU of start timing for fuel gas injection, and the time for the injection valve to stay open. If the GCCU receive a signal ready from the safety system and GCCU observes no abnormalities then the injection of fuel gas will starts at the relevant crankshaft position.

The GSSU, fuel gas System Monitoring and Control

The GSSU performs safety monitoring of the fuel gas System and controls the fuel gas Shut Down.

It monitors the following:

• Status of exhaust gas temperature

• Pipe ventilation of the double wall piping

• Sealing Oil pressure

• Fuel gas Pressure

• GCSU ready signal

If one of the above parameters, referring to the relevant fuel gas state differs from normal service value, the GSSU overrules any other signals and fuel gas shut down will be released.

After the cause of the shut down has been corrected the fuel gas operation can be manually restarted.

GCSU, PMI on-line

The purpose of the GCSUs is to monitor the cylinders for being in condition for injection of fuel gas. The following events are monitored:

• Fuel gas accumulator pressure drop during injection

• Pilot oil injection pressure

• Cylinder pressure:

Low compression pressure Knocking

Low Expansion pressure

• Scavenge air pressure

If one of the events is abnormal the ELGI valve is closed and a shut down of fuel gas is activated by the GSSU.

Safety remarks

The primary design target of the dual fuel concept is to ensure a Dual Fuel Control System which will provide the highest possible degree of safety to personnel. Consequently, a failure in the gas system will, in general, cause shut down of fuel gas running and subsequent purging of pipes and accumulators

Fuel gas operation is monitored by the safety system, which will shut down fuel gas operation in case of failure. Additionally, fuel gas operation is monitored by the Plant Control and the Fuel Control, and fuel gas operation is stopped if one of the systems detects a failure. As parameters vital for fuel gas operation are monitored, both by the Plant Control/ Fuel Control and the Safety Control System, these systems will provide mutual back-up.

Conclusion

The above chapters reveal the differences in principle and service experiences of Latest Marine two stroke Engines in the Shipping Industry. Developments in the Marine engines gives the advantages to the Owners as well as the Operators with High Efficiency, Lower Fuel consumption, Better maneuverability, Ease of Maintenance and  Lower Emissions.  Continuous Research and development is ongoing to achieve, the future Marine Environmental Protection standards for  Cleaner Oceans and Safer Ships.

Abbreviations

BIBLOGRAPHY

[1] P. Sunn Pedersen: “Development Towards the Intelligent Engine”, 16th International Marine Propulsion Conference, London 10-11 March 1994, Proceedings pp 77-88

[2] P. Sørensen & P. Sunn Pedersen: “The Intelligent Engine and Electronic Products - A Development Status”. Proceedings of the 22nd CIMAC International Congress on Combustion Engines, Copenhagen 18-21 May 1998, pp 551-564

[3] ‘Utilisation of VOC in Shuttle Tankers’, MAN B&W Diesel A/S, company publication P.342-98.11, 1998 (25 pages)

[4] P. Sunn Pedersen & P. Sørensen: ‘Computer Controlled System for two-stroke Machinery (A Progress Report)’. 22nd Marine Propulsion Conference, Amsterdam 29-30 March 2000. Conference Proceedings, pp 17–33.

[5] H.SAKABE and M.OKABE, The UEC-LSⅡ/LSE Engine Development Program, CIMAC 2001, pp. 28-37

[6] S.LAULISTEN, J.DRAGSTED, and B.BUCHOLZ, Swirl  Injection Lubrication, CIMAC 2001, pp. 921-932

[7] H.SAKABE and K.SAKAGUCHI, The UEC Engine Development Program and Its Latest Development, CIMAC Kyoto 2004

[8] K.SAKAGUCHI and M.SUGIHARA, The Development of the Electronically Controlled Engine “MITSUBISHI UEC Eco-Engine,” CIMAC Kyoto 2004

[9] “LNG Carriers with Low Speed Diesel Propulsion”, Ole Grøne, The SNAME Texas Section14th Annual Offshore Symposium, November 10, 2004, Houston, Texas

[10] “Basic Principles of Ship Propulsion”, p.254 – 01.04, January 2004, MAN B&W Diesel A/S

[11] “ME-GI Engines for LNG Application” System Control and Safety Feb. 2005 Ole Grøne, Kjeld Aabo, Rene Sejer Laursen, MAN B&W Diesel A/S Steve Broadbent,Flotech

[12]      Wartzila  NSD website

13]       Man  B & W  Website