Effects of Mixture Preparation on HC Emissions of a S.I. Engine Operating Under Steady-State Cold Conditions

The effects on engine-out HC emissions of a premixed propane system, and three PFI systems employing different types of injectors and using Phase II gasoline were investigated on a four-cylinder DOHC spark-ignition engine. Cold conditions resulted in significant increases in engine-out HC emissions. Phase II gasoline caused much higher emissions of HC than propane fuel. The difference in the HC emissions from the two fuels increased dramatically with lowering the coolant temperature of the engine. At cold conditions, liquid fuel entering the combustion chamber appears to be the primary source of engine out HC emissions. At the coldest temperature tested the estimated percent contribution of in-cylinder liquid fuel to the observed increase of HC emissions was as much as 96%.