4. Cycles with supercharging

Supercharging an engine allows air (diesel engines) or a mixture (gasoline engines) to be introduced at a higher pressure than atmospheric pressure. This means that, for a given cubic capacity and intake temperature, more mixture, and therefore more fuel, can be introduced at each intake. Thus, for a given engine speed, engine power is increased. The first applications of this technique were in aircraft engines, where atmospheric pressure drops with altitude, resulting in a loss of engine power.

Pressurization prior to admission to the cylinders is performed either by a piston compressor or, more commonly today, by a centrifugal compressor. In the former case, the compressor is driven directly by the crankshaft; in the latter, it is usually driven by a turbine using the residual energy in the engine exhaust gases. The combination of turbine and compressor is known...