Why is the bmep lower at the maximum rated power for a given engine than the bmep at maximum torque?
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One reason is that friction increases with engine speed and friction at rated power is significantly higher than at peak torque speed. BMEP = IMEP - FMEP therefore if IMEP (measure of work done in the cylinder) were the same at both rated power and at maximum torque (which would require the same volumetric and indicated thermal efficiencies at both conditions) then the higher friction (FMEP) at rated power would result in a lower BMEP.
A second factor is that volumetric efficiency is typically higher at maximum torque than at rated power primarily due to intake and exhaust tuning in a naturally aspirated engine or increased turbocharger efficiency in a turbocharged engine. This results in higher IMEP at maximum torque than at rated power with correspondingly higher BMEP
A second factor is that volumetric efficiency is typically higher at maximum torque than at rated power primarily due to intake and exhaust tuning in a naturally aspirated engine or increased turbocharger efficiency in a turbocharged engine. This results in higher IMEP at maximum torque than at rated power with correspondingly higher BMEP
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