Pmax & Mean Effective Pressure: The Relationship Explained

In summary, the relationship between maximum pressure (p max) and mean effective pressure inside the cylinder can be determined from the PV diagram for the diesel cycle. The formula for mean effective pressure (P) is (BHP = P*L*A*N) / 33,000, where P is in psi, L is the piston stroke in feet, A is the area of the piston in square inches, and N is the number of power strokes per minute. This equation can be used to calculate the power potential of an engine by assuming a similar or the same mean effective pressure.
  • #1
Mohamed Youssef
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What is the relation between p max and mean effective pressure inside the cylinder
 
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  • #2
Mohamed Youssef said:
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
 
  • #3
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.
 

FAQ: Pmax & Mean Effective Pressure: The Relationship Explained

What is the definition of Pmax?

Pmax, or maximum pressure, is the highest pressure that is reached during the combustion process in an internal combustion engine.

What is Mean Effective Pressure (MEP)?

MEP is a measure of the average pressure that is exerted on the piston in an internal combustion engine over the entire power stroke.

How are Pmax and MEP related?

Pmax and MEP are directly related to each other, as they both represent different aspects of the combustion process in an engine. Pmax is the peak pressure, while MEP is the average pressure over the entire power stroke.

Why is the relationship between Pmax and MEP important?

The relationship between Pmax and MEP is important because it can provide valuable insights into the performance and efficiency of an engine. A higher Pmax and MEP can indicate a more powerful and efficient engine.

How can Pmax and MEP be measured?

Pmax and MEP can be measured using specialized equipment such as a pressure transducer, which can directly measure the pressure inside the engine cylinder during the combustion process. These measurements can then be used to calculate Pmax and MEP.

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