TURBOCHARGING

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Centrifugal Blower:

It has a high-speed wheel provided with vanes and enclosed in a carefully shaped casing (volute). Air entering the wheel near the hub is thrown outward by centrifugal force. The volute is so shaped that the high velocity of the air is transformed into pressure. Centrifugal blowers run at relatively high speeds (more than 4000 - 5000 rpm) and are, therefore, driven more readily from a separate motor or a turbine rather than from engine.

The positive displacement rotary blower finds particular favor in applications where the blower is driven by an engine, which is required to deliver full torque over a wide-speed range (as in automotive service). Its advantage over an engine driven centrifugal blower in such applications is that the positive displacement blower delivers practically the same amount of air per revolution regardless of speed or working pressure. A centrifugal blower, on the other hand, develops a pressure proportional to the square of the speed; hence a centrifugal blower driven by the engine itself (through gears etc.) would supply little air when the engine speed is reduced.

Turbochargers:

These are high-speed centrifugal blowers usually driven by a gas turbine that utilizes the kinetic energy of exhaust gases.  They are widely used on modern marine diesel engines because they run largely on power that would otherwise be wasted. About 35% of total heat energy in fuel is discharged to the exhaust gases.  By utilizing this power to run turbine, which runs a centrifugal compressor usually fitted on same shaft, the power of engine can be increased by increasing the pressure and density of air charge.   This is the essential principle of exhaust turbo-charging.  About 20% of this potential “waste energy” can be recovered by exhaust turbo-charging.

The Turbo blower comprises a gas turbine, driven by the engine exhaust gases, direct coupled to a compressor, i.e. a blower, which draws air from the ambient atmosphere and discharges to the air inlet manifold on the engine. The power generated in the turbine must equal that required by the compressor. Turbocharger is usually independent (mechanically) of engine. Its only connections to the engine are the exhaust pipe to turbine and air pipe from the blower to the intake system of engine.  A diagrammatic arrangement is shown in figure below.