Cycle-by-Cycle Variations in Spark Ignition Engine Combustion - Part II: Modelling of Flame Kernel Displacements as a Cause of Cycle-by-Cycle Variations

A review of cycle-by-cycle variations in combustion and early flame histories is used to discuss the origins of cyclic variations in spark ignition engines. The hypothesis that cyclic variations are caused by the displacement of the flame kernel, is tested by means of a phenomenological turbulent entrainment combustion model. The model results are compared with experimental cycle-by-cycle combustion data, from a range of operating conditions that covers changes in: fuel, air fuel mixture, ignition timing and throttle setting. The combustion is characterised by the cycle-by-cycle variations in: the indicated mean effective pressure, the maximum pressure, the maximum rate of pressure rise, the burn rate and the flame speed. The model predicts correctly the effect of changes in the engine operating point on the cycle-by-cycle variations in combustion, and in many cases there is also good numerical agreement.

This study concludes that displacement of the flame kernel during the early stages of combustion, has a major part in the origination of cycle-by-cycle variations in combustion.