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2.7 Mean Effective Pressure
Mean Effective Pressure (MEP). It is a fictitious pressure that, if it acted on the piston during the entire power stroke, would produce the same amount of net work as that produced during the actual cycle.
* The net work output of a cycle is equivalent to
the product of the mean effective pressure and
the displacement volume.
Wnet = MEP * Piston area * Stroke = MEP * Displacement volume
Wnet
MEP = -----------------------------------------
Vmax - Vmin
The mean effective pressure can be used as a parameter to compare the performances of reciprocating engines of equal size. The engine with a larger value of MEP delivers more net work per cycle and thus performs better.
Reciprocating engines are classified as :
* Spark-ignition (SI) engines
* Compression-ignition (CI) engines
depending on how the combustion process in the cylinder is initiated. In SI engines, the combustion of the air–fuel mixture is initiated by a spark plug . In CI engines, the air – fuel mixture is self-ignited as a result of compressing the mixture above its selfignition temperature.
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