Regulation 18 Fuel Oil Quality

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In an attempt to reduce the problems of poor quality fuel affecting air pollution, this regulation has attempted to reduce the increasing problem of waste dumping in marine residual fuel oils. The wording and detail of the regulation should be defined enough to of real use, but as recent decisions have shown, this needs to be tested in a Court of Law before everybody fully understands and obeyed its requirements. The regulation states that the fuel oils:

a)         Be a blend of hydrocarbons derived from petroleum refining.

b)         Be free from inorganic acids

c)         Shall not include added substances or chemical waste which

i)          jeopardises the safety of the ship, or effects the performance of the machinery

ii)         is harmful to personnel, or

iii)        contributes to overall air pollution

The bunker note must contain a declaration that the fuel conforms to the requirements stated above. These bunker notes must be available for inspection by Port Authorities.

Carbon Monoxide

CO is formed due to the incomplete combustion of organic material where the oxidation process does not have enough time to occur completely. This toxic gas is unlikely to be produced in large concentrations in diesel engines that have a large excess oxygen. This compound can still be burnt to form CO₂, and is usually only present when pockets of excess fuel are present, hence higher levels may indicate inefficient fuel atomisation or penetration.

Carbon Dioxide

Co₂ is not toxic however, it has been linked to the greenhouse effect and global warming.

It is one of the basic products of combustion and the only viable method of reduction is to reduce the quantity of fuel burned. Diesel engines currently meet the guidelines.

Hydrocarbons

This is the small quantity of fuel, which leaves the cylinder unburnt due to insufficient temperature, which can occur near the liner wall (wall quenching). It is dependant upon the type of fuel used, and if fuel preparation and combustion is efficient, then this emission quantity should be small.

Particle emission or smoke

Particle emission, as well as hydrocarbons are thought to be carcinogenics.

The limit of smoke allowable is determined by different methods, i.e. smoke numbers (which express the degree of blackening on a white filter paper, Bosch or Bacharach), or smoke values (which quantifies the reduction in light passing through the exhaust plume, Hartridge or Ringelmann).

This exhaust plume is more visible on the larger engines, as the plume has a larger diameter. The particles may be due to a number of sources:-

            a)         agglomeration of very small (1µm) particles of partly burnt fuel,

            b)         ash content of fuel oil and cylinder oil,

            c)         partly burnt lube oil,

            d)         combustion chamber/exhaust system deposits peeling off.

Soot for source a) (responsible for 90%) is produced during the combustion process by pyrolysis (burning without visible flame). This consumes the lighter fractions of the fuel, leaving a hard shell that is slow to burn, and hence would be exhausted as soot. Soot levels increase when diffusion combustion is prominent.

Soot levels will also be increased when any the following are present:-

·         Slow burning fuel present with:-

i)          High asphaltene fuels. The fuel combusts much later and thus consumption of soot is reduced,

            ii)         Fuel on liner wall. This will cause the fuel to burn slowly as droplet temperatures will be low.

            iii)        Larger droplets of fuel (poor atomisation). This reduces the rate of diffusion combustion, and hence makes the fuel slower burning.

·         Increased cylinder temperatures present when:-

            i)          Scavenge temperatures are high. Increasing the inlet temperatures from 20 to 100^oC will increase smoke levels by 50%. This is probably due to increased pyrolysis, hence the fuel is being `baked' instead of consumed.

Remember that soot is not only a pollutant, but it will collect in the uptakes mainly on the cooler surfaces, especially if `wet' with oil, and increase exhaust gas boiler back pressure and increase the possibility of boiler fires.