What should be the mean effetive pressure ?

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Discussion Overview

The discussion revolves around calculating the Indicate Mean Effective Pressure (IMEP) for a 4-stroke, single-cylinder engine operating on a constant volume cycle. It includes aspects of engine performance, mechanical efficiency, and thermodynamic principles.

Discussion Character

  • Homework-related
  • Technical explanation

Main Points Raised

  • One participant presents a problem involving an engine's brake power, mechanical efficiency, compression pressure, and maximum pressure, seeking to calculate the IMEP.
  • Another participant emphasizes that homework questions should be directed to the relevant forum and suggests that quick responses may not be guaranteed.
  • A different participant describes the mean effective pressure as a theoretical constant pressure that would produce the same work as the actual engine cycle, providing a formula for MEP calculation.
  • There is a mention of needing to determine the work done in one cycle and the displacement volume to calculate MEP, referencing air standard analysis methods.

Areas of Agreement / Disagreement

Participants generally agree on the definition and importance of mean effective pressure in engine performance, but there is no consensus on the specific calculation steps or the appropriateness of the forum for the question.

Contextual Notes

Some assumptions regarding the engine's operation and the definitions of terms like displacement volume and work done may not be fully articulated. The discussion does not resolve the mathematical steps required for the calculation.

falik
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A 4 stroke, single cylinder engine working on constant volume cycle, developes 7.5 KW brake power at 60 rev/sec the mechanical efficiency being 80%. The pressure at the beginning of compression is 0.97 bar, the engine has a volumetric compression ratio of 7 and the maximum pressure reached in the cycle is 34 bar. If both compression and expansion is according to the law PV= costant where n=1.38, calculate Indicate Mean Effective Pressure ?
 
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bump ! anyone ?
 
Homework questions are best answered in the relevant forum. Also, if you're expecting an answer within 7 hours of posting a question, you may be disappointed.
 
It is presure that is mesured on the "motor table" (i don' know how to say in english, maybe dyno table?).
 
Please refer all future HW questions to the HW Forum. Anyway...

The mean effective pressure (MEP) is the theoretical constant pressure that if acted one the piston for the entire stroke would produce the same amount of work actually developed. This can be shown mathematically as:

MEP = net work for one cycle / displacement volume

You first need to determine the work created from one cycle. Then using either the air standard analysis or the cold air standard analysis you need to work backwards to determine the displacement volume of the engine. Once those two parameters are found, you can then easily find the MEP.
 

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