Pmax & Mean Effective Pressure: The Relationship Explained

[Mohamed Youssef]

What is the relation between p max and mean effective pressure inside the cylinder

 

[Andrew Mason]

What is the relation between p max and mean effective pressure inside the cylinder

Welcome to PF Mohamed!

The relationship between pressure (ie. the pressure inside the cylinder between piston and end of cylinder) and volume (volume of the cylinder between the piston and end of cylinder) can be determined from the PV diagram for the diesel cycle.

If by "p max" you mean the maximum pressure attained, that is easily determined from the highest point in the PV diagram (i.e. 2-3).

AM

 

[dean barry]

Heres an old equation including (brake) mean effective pressure (P):
(P would appear to be akin to average pressure)
BHP = ( P*L*A*N ) / 33,000
P = bmep in psi
L = piston stroke in feet
A = area of piston in sq ins
N = number of power strokes per minute

Basically, its the work done in 1 minute / the official work done by 1 BHP
( 1 BHP = 33,000 lbsforce - ( feet / min ) )

If you had the crank BHP, you could derive the value for P if you know the remaining figures, so:
P = ( 33,000 * BHP ) / ( L*A*N )

Its a handy value to know if you need to calculate the power potential of another engine by assuming the bmep to be similar or the same.