Mean effective pressure of Engine

Based on computed or observed power, Mean effective pressure is the average pressure inside the cylinders of an internal combustion engine. When the manifold pressure rises, Mean effective pressure rises as well.

A specific indicated mean effective pressure (IMEP) and the corresponding brake mean effective pressure  (BMEP) will exist for a particular engine running at a certain speed and power output. These are derived, respectively, from indicated power and brake power. 

Indicated mean effective pressure can be written as:

pim – (60000 x ip) /LAnK

Similarly

Brake mean effective pressure can be written as:

pbm – (60000 x bp) /LAnK

Where –

ip – Indicated power

pim – Indicated mean effective pressure

L – Length of stroke

A – Area of piston

N- Revolution per minute

n – Number of power stroke

K – Number of cylinders

Knowing the engine indicator diagram is another approach to determine the indicated mean effective pressure (PV diagram).

pim – Area of indicator diagram / Length of indicator diagram

Where difference between total volume and clearance volume gives length of indicator diagram.