# Mean effective pressure in a diesel engine

• Monsterboy
In summary, the conversation discusses the density of air entering a diesel engine, the compression ratio, air intake and net work output at steady state, and the mean effective pressure. The equations for mean effective pressure, compression ratio, stroke volume, clearance volume, efficiency, and mass flow rate are also mentioned. The attempt at a solution calculates the efficiency, heat supplied, volume flow rate, and mean effective pressure, but the final result does not match the given answer.
Monsterboy

## Homework Statement

Air enters a diesel engine with a density of 1.0 kg/m3. The compression ratio is 21 .At steady state ,the air intake is 30 x10-3 Kg/s and the net work output is 15 kW .The mean effective pressure (in kPa) is ...

## Homework Equations

Pm= W.D/ Vs
C = V1/V2
V1 =Vs +Vc
V2=Vc

##\eta## = 1- ##\frac{1}{r^(\gamma-1)} \frac{ \rho^\gamma-1}{(\rho-1)\gamma}##
Pm -mean effective pressure
W.D -work done
Vs -stroke volume
Vc-clearance volume
##\gamma## -ratio of specific heats.
##\rho## -density (rho)
##\eta## -efficiency (eta)
Mass flow rate -m.
C- compression ratio

## The Attempt at a Solution

[/B]
Since density is 1 kg/m3 ,the efficiency becomes 100% according to the formula.
because there is a (rho-1) term in the denominator of the second term.

If the above is correct then W.D =Heat supplied = 15kW

So m. /density = Volume flow rate = Vs ?

if r= 21 ,then Vs =20Vc

So volume flow rate = 30x10-3 = Vs ?

So mean effective pressure =15000W/(30x10-3)
= 500 kPa
Is the above calcualtion correct ?
but the answer given to me is 525 kPa

Last edited by a moderator:
I just want to know whether my calculation is right because i am not getting the answer i was given.

Oops! rho is not density , it is cut-off ratio.

## What is the definition of mean effective pressure (MEP) in a diesel engine?

Mean effective pressure (MEP) is a measure of the average pressure that is exerted on the piston in a diesel engine during the power stroke.

## How is mean effective pressure calculated in a diesel engine?

MEP can be calculated by dividing the work done by the engine during the power stroke by the displacement volume of the engine. It is typically measured in units of pressure, such as pounds per square inch (psi) or kilopascals (kPa).

## What factors can affect the mean effective pressure in a diesel engine?

The mean effective pressure in a diesel engine can be influenced by a number of factors, including the compression ratio, fuel injection timing, air-fuel ratio, and engine speed. Changes in any of these variables can impact the amount of pressure generated in the cylinder during the power stroke.

## Why is mean effective pressure important in diesel engine performance?

MEP is an important indicator of engine performance because it directly affects the amount of work that the engine can produce. Higher MEP values can result in increased power output and efficiency, while lower MEP values can lead to decreased performance and potential engine damage.

## How can mean effective pressure be optimized in a diesel engine?

To optimize mean effective pressure in a diesel engine, engineers may adjust various engine parameters such as compression ratio, fuel injection timing, and air-fuel ratio. Additionally, regular maintenance and tuning of the engine can help to ensure that MEP is at its optimal level for maximum performance and longevity.

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