Correlation Between Knock Intensity and Heat Transfer Under Light and Heavy Knocking Conditions in a Spark Ignition Engine

Instantaneous piston surface temperatures and heat flux rates were measured inside and outside the end-gas zone of a single-cylinder research engine operated under light and heavy knocking conditions. The engine was run with center and rear side spark-plug configurations, thus alternating the position of the heat flux probes relative to the end gas. Heat transfer data were collected over 88 engine cycles for each of which knock intensity was determined by heat release analysis. Under light knock, the ensemble-averaged peak heat-flux at locations near the end-gas increased with spark advance towards heavier knock, showing significant departure from its trend prior to the onset of knock. Under heavy knock, the ensemble-averaged peak heat-flux increased throughout the piston crown. Despite showing significant scatter, individual cycle, peak heat-flux values near the end-gas region were found to follow an increasing trend with knock intensity under light knocking conditions. In the case of heavy knock, individual cycle peak heat-flux near the end-gas zone showed more noticeably increasing trends with quite narrow scatter, especially for a stoichiometric air-fuel ratio. The increase in heat transfer due to heavy knock was also revealed by the high statistical correlation between peak heat-flux and autoignition indices.