Effects of Engine Cooling Strategy on Knock Suppression in High-Compression Ratio Spark-Ignition Engine

Abstract

Increasing the compression ratio is one of the methods to increase the thermal efficiency of a gasoline spark-ignition (SI) engine. However, this exposes the end-gas to thermodynamic conditions that are prone to cause spontaneous ignition. The resulting knock acts as a barrier to the thermal efficiency improvement, and thus, may offset the thermal efficiency benefit of the high compression ratio. In this study, performance and knock characteristics with different coolant flow directions and coolant temperatures were evaluated in a port fuel injection SI gasoline engine with a compression ratio of 14. The coolant temperature was reduced to suppress the knock. Although the knock was accordingly suppressed, the fuel consumption increased because of the increase in the heat loss. From a knock sensor analysis, the knock was mainly found in the exhaust side. Therefore, the coolant flow direction from the intake to the exhaust in the baseline engine head was changed to the opposite direction in a modified engine head for suppressing the knock in the exhaust side. The change in the coolant flow direction resulted in knock suppression as well as fuel consumption reduction. © 2022, KSAE.