The Influence of Coolant Temperature on Unburned Hydrocarbon Emissions from Spark Ignition Engine

A study has been initiated to understand the influence of coolant temperature on HC emissions employing a dual system cooling the cylinder head independently from the engine block. Especially, we have studied its influence on post-oxidation, fuel absorption-desorption, crevice volumes and fuel-air mixture preparation. The results show that the cylinder head temperature has more influence on HC emissions than the block temperature. It was also found that mixture preparation, absorption/desorption and crevice volumes with commercial gasoline is greatly improved by the cooling temperature. The post-oxidation process is also reduced for a decrease of the coolant temperature from 90°C to 35°C.