Effect of coolant water and intake air temperatures on thermal efficiency of a spark ignition engine

An improvement of thermal efficiency is strongly demanded for gasoline engines. In this study, experiments were carried out to investigate the effects of intake air temperature and coolant temperature on brake thermal efficiency, heat loss and friction loss in a spark ignition gasoline engine. Experimental results showed that, intake air temperature has a little effect on brake thermal efficiency during partical load operation. During high load operation, a decrease in intake air temperature improved brake thermal efficiency due to an improvement in indicated thermal efficiency and decrease in exhaust loss. It was also revealed that the combination of high temperature cooling water for the engine block and low temperature cooling water for the cylinder heat is effective for improving brake thermal efficiency.