Heat-flux measurements were obtained at several locations on the cylinder head and liner of a four-stroke, single-cylinder, spark-ignition engine. The variations of heat transfer with air-fuel ratio and volumetric efficiency were investigated. The magnitude of the heat flux was found to be highest at near-stoichiometric composition, whereas at either leaner or richer composition the heat flux decreased. An increase in volumetric efficiency from 40 to 60 percent resulted in an increase in peak heat flux of about 30 percent. The largest cycle-to-cycle variation in the measured heat flux occurred at the time of the initial high rate of heat flux. This is related to the cycle-to-cycle variation of flame propagation in the combustion chamber. Finally, the calculated amount of heat transferred to the walls of the combustion chamber during the closed portion of the engine cycle (intake valve closing to exhaust valve opening) agreed with the corresponding values obtained from the heat-flux measurements.

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