Power Plant Engineering

8.12 SUPERCHARGING SYSTEM OF DIESEL POWER PLANT
The purpose of supercharging is to raise the volumetric efficiency above that value which can be
obtained by normal aspiration.
Since the I.H.P. produced by an I.C. engine is directly proportional to the air consumed by the
engine. And greater quantities of fuel to be added by increasing the air consumption permit and result in
greater power produced by the engine. So, it is, therefore, desirable that the engine should take in the

---

248
POWER PLANT ENGINEERING
greatest possible mass of air. The supply of air is pumped into the cylinder at a pressure greater than the
atmospheric pressure and is called supercharging. When greater quantity of air is supplied to an I.C.
engine it would be able to develop more power for the same size and conversely a small size engine fed
with extra air would produce the same power as a larger engine supplied with its normal air feed.
Supercharging is used to increase rated power output capacity of a given engine or to make the rating
equal at high altitudes corresponding to the unsupercharged sea level rating. Installing a super charger
between engine intakes does supercharging and air inlet through air cleaner super charger is merely a
compressor that provides a denser charge to the engine thereby enabling the consumption of a greater
mass of charge with the same total piston displacement. Power required to drive the super charger is
taken from the engine and thereby removes from over all engine output some of the gain in power
obtained through supercharging.
Since the main object of supercharging is to increase the power output of these engine without
increasing its rotational speed or the dimensions of the cylinder. This is achieved by increasing the
charge of air, which results more burning of the fuel and a higher mean effective pressure. So there are
three possible methods that increase the air consumption of an engine,
1.To increasing the piston displacement, but this increases the size and weight of the engine, and
introduces additional cooling problems.
2.Running the engine at higher speeds, which results in increased fluid and mechanical friction
losses, and imposes greater inertia stresses on engine parts.
3.Increasing the density of the charge, such that a greater mass of charge is introduced into the
same volume or same total piston displacement.