The mean effective pressure is a quantity relating to the operation of a reciprocating engine and is a valuable measure of an engine's capacity to do work that is independent of engine displacement.
Brake mean effective pressure (BMEP) - Mean effective pressure calculated from measured brake torque.
Gross indicated mean effective pressure (IMEPg) - Mean effective pressure calculated from in-cylinder pressure over compression and expansion portion of engine cycle (360° in a four-stroke, 180° in a two-stroke). Direct measurement requires cylinder pressure sensing equipment.
Net indicated mean effective pressure (IMEPn) - Mean effective pressure calculated from in-cylinder pressure over the complete engine cycle (720° in a four-stroke, 360° in a two-stroke). Direct measurement requires cylinder pressure sensing equipment.
Pumping mean effective pressure (PMEP) - Mean effective pressure from work moving air in and out of the cylinder, across the intake and exhaust valves. Calculated from in-cylinder pressure over intake and exhaust portions of engine cycle (360° in a four-stroke, 0° in a two-stroke). Direct measurement requires cylinder pressure sensing equipment. PMEP = IMEPg - IMEPn.
Friction mean effective pressure (FMEP) - Theoretical mean effective pressure required to overcome engine friction, can be thought of as mean effective pressure lost due to friction. Friction mean effective pressure calculation requires accurate measurement of cylinder pressure and dynamometer brake torque. FMEP = IMEPn - BMEP.