The pressure in an engine varies greatly throughout one cycle of operation. Hence the pressure that is used to calculate indicated power is the mean effective pressure. IMEP is equal to brake mean effective pressure (BMEP) plus friction mean effective pressure (FMEP). The below section shows you the indicated mean effective pressure formula to calculate the IMEP (Indicated mean effective pressure) of an engine. Here the mean effective pressure calculation depends on the integration of pressure and volume diagram.

Where,

IMEP = Indicated Mean Effective Pressure

A = Area of Indicator Diagram

L = Base Length of Indicator Diagram

C = Constant

The indicated mean effective pressure formula can also be derived from harmonic analysis of pressure waveform in working space, instead of conventional numerical integration of the pressure ± volume (P±V) diagram.