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## Main Question or Discussion Point

I have a P-V trace for a wide open throttle and a part load. Is it possible to calculate the BMEP from these graphs?

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I have a P-V trace for a wide open throttle and a part load. Is it possible to calculate the BMEP from these graphs?

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Ranger Mike

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BMEP = ( Hp x 13000) / ( liter displacement x RPM)

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that doesnt really help considering all i am given are values of different pressures and volumes

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Q_Goest

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For example, if you have a table of values that give pressure and volume, you should be able to take average pressure (gage pressure, not absolute) and change in volume, multiply to obtain work, then sum all work done over a single cycle (360 degrees of crankshaft rotation for a 2 stroke, 720 degrees for a 4 stroke) and divide by time it takes for that cycle to get power.

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brewnog

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Sure, integrate to find the area enclosed by the PV curve; this gives you the IMEP.

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Integrating real curves is a *****, either find a program that can make approximate curves from a set of data points or break out the graph paper.

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If you have no better software than Excel, you can use a trapezoidal numerical integration approach reasonably well so long as the x-interval is pretty small compared to the sample length.Integrating real curves is a *****, either find a program that can make approximate curves from a set of data points or break out the graph paper.

But when it comes to a manual method, use a planimeter! I've mentioned before with PV diagrams, they're absolutely fantastic and much better than counting squares :)

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- #9

Q_Goest

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Actually, if you used the average pressure between two datapoints then you used the trapezoid rule! :)

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