The process of increasing the inlet air or charge density in order to increase the power output of the engine is called supercharging. The device used for increasing the pressure of air above atmospheric pressure is called supercharger.

Effect of Supercharging:

The induced charge by the supercharger during suction helps in better mixing of fuel and air during its compression stroke due to the turbulent effect created by the supercharger and the increased temperature helps in vaporisation of fuel.

The increase in temperature of charge, however, reduces the charge density and it is detrimental in case of S.I. engine since it develops the tendency to detonation.

Another effect of supercharging is that the power is required to drive the supercharger except in case if turbocharger, which it usually driven by the engine consequently, it partly offset the gained power output due to supercharging.

Fig. 1. Shows the difference between the theoretical (p-V) diagram of a naturally aspirated (unsupercharged) engine and the supercharged engines the difference between the two are:

(a) Increased pressure over the naturally aspirated engine cycle.

(b) Pumping loop of supercharged engine is positive, therefore, the work output equivalent to this area is to be added instead of being subtracted.

For naturally aspirated engine,

For supercharged engine,

Therefore, we get increased indicated mean effective pressure with supercharged engine, it is due to the increased amount of air inducted during the section process. It results into increased power output of the engine.