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This paper addresses issues associated with the accurate determination of indicated mean effective pressure (imep) for internal combustion engines. Items covered include a comparison of alternative imep equations and the effects of crank angle resolution, signal noise, thermal shock, crank angle phasing and connecting rod length errors. The best imep equation to use has been identified and the magnitude of errors under a wide range of conditions quantified. The results show that inaccuracy in the calculated imep will mainly be caused by thermal shock and errors in the crank angle phasing and transducer sensitivity. In contrast, the effects of coarse crank angle resolution, incorrectly specified connecting rod length, signal noise and integration period error should be relatively small.

This paper addresses issues associated with the accurate determination of gross heat release energy. The magnitude of analysis and measurement errors has been quantified using simulated and measured gasoline engine pressure data. This has revealed that calculated gross heat release is very sensitive to the assumed ratio of specific heats, charge to wall heat transfer and pressure data errors. Two improved heat release models have been proposed and further investigated and shown to generally give good performance for specific applications although further work is required to fully quantify their accuracy.