Overall Volumetric Efficiency:

By considering the effect of wire-drawing at the valves, re expansion, polytropic compression & leakage, we can write the expression for the overall or net volumetric efficiency as described

 The technique of getting better the volumetric efficiency includes the following:

(a) By providing clearance as small as possible,

(b) Maintaining low pressure ratio,

(c) Cooling throughout compression,

(d) Decreasing pressure drops at the valves by designing a light- weight valve method, minimizing valve overlaps and selecting suitable lubricating oils.