This paper describes a means of monitoring cyclic variability in reciprocating engines that is an alternative to cylinder pressure measurements. The monitoring system uses robust exhaust temperature sensors that are capable of detecting cycle-to-cycle variations in the gas temperatures near each exhaust port. These variations are related to cyclic variations in combustion, and tend to increase as cyclic variability worsens. Further processing yields a combustion variability signal that is intended to reflect relative changes in the Coefficient of Variation of Indicated Mean Effective Pressure (COV of IMEP). Proof of concept experiments have been carried out using a naturally aspirated, propane fueled automotive engine equipped with laboratory grade in-cylinder pressure transducers. The results show a good correlation between the exhaust cyclic variability signal and the COV of IMEP from cylinder pressure measurements.

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