Mean Effective Pressure

on . Posted in Classical Mechanics

Mean effective pressure, abbreviated as MEP, is the average pressure that acts on the piston of an engine during a complete combustion cycle.  MEP is equal to the difference between the indicated pressure and the exhaust pressure, divided by the clearance volume.  The indicated pressure is the pressure measured by a pressure gauge, while the exhaust pressure is the pressure measured in the exhaust system of the engine.  The clearance volume is the volume that remains in the combustion chamber after the piston has reached the end of its compression stroke. 

The MEP is an important parameter that is used to evaluate the performance of an engine. It is related to the power output of the engine, and a higher MEP generally indicates a more efficient engine.  The MEP formula can be used to optimize the design of an engine, by adjusting the various parameters such as the compression ratio, fuel injection timing, and valve timing, to achieve the desired MEP.


Mean Effective Pressure formula

\( MEP =   p_i - p_e \;/\; V_c \)     (Mean Effective Pressure)

\( p_i =  p_e + MEP \; V_c  \)

\( p_e =  p_i - MEP \; V_c  \)

\( V_c =  p_i - p_e \;/\; MEP \)

Symbol English Metric
\( MEP \) = mean effective pressure \(lbf\;/\;in^2\) \(Pa \)
\( p_i \) = indicated pressure \(lbf\;/\;in^2\) \( Pa \)
\( p_e \) = exhaust pressure \(lbf\;/\;in^2\) \( Pa \)
\( V_c \) = clearance volume \( ft^3 \) \( m^3 \)

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Tags: Pressure Engine