Can the Mean Effective Pressure MEP of an automobile engine

Can the Mean Effective Pressure (MEP) of an automobile engine be less than atmospheric? How do you know?

Solution

No. The Mean Effective Pressure of an automobile engine in general cannot be less than atmospheric pressure.

The opertion of the engine depends on the pressure difference between the top and bottom sides of ech piston. This can be done either by suplying heat energy or by extracting the heat energy from the engine. However the later is very difficult which is the case of Mean effecetive pressure less than atmospheric pressure. Since extracting heat energy from the engine is not an easy process but where as the former is easy and this is the case where the Mean Effective Pressure is greater than the atmospheric pressure. Higher the mean effective pressure, more is the efficiency.