The Effects of Intake-Flow Configuration on the Heat-Release and Heat-Transfer Characteristics of a Single-Cylinder Four-Valve S.I. Engine

Local transient heat-flux measurements and heat-release analyses were employed to investigate the effects of introducing swirl or tumble fluid motion during the intake stroke on the combustion and heat-transfer characteristics of a single-cylinder spark-ignition engine. In general, swirl or tumble motion decreased the period of flame development and increased the peak rate of heat release, but, surprisingly, it increased the period of combustion. The latter increase was the result of comparatively low rates of fuel burning during the last stages of combustion. Swirl or tumble motion also significantly increased the local heat flux on the cylinder head. The highest peak heat flux was obtained for tumble motion. The observed increase in heat flux is attributed to the resultant increase in the mean velocity and in the turbulent intensity of the gases in the combustion chamber, which, in turn, augment the rate of heat release and the effective convective heat-transfer coefficient. Finally, the local heat-flux measurements were compared with corresponding area-averaged heat fluxes computed using a suitably scaled empirical heat transfer correlation proposed by Woschni. The peak value of the computed area-averaged heat flux was in fair agreement with the corresponding values measured in the central region of the combustion chamber. On the other hand, the crank angle at which the computed peak heat flux occurred was in good agreement with the corresponding result measured at the outer location in the periphery of the combustion chamber.