Contribution of Liquid Fuel to Hydrocarbon Emissions in Spark Ignition Engines

The purpose of this work was to develop an understanding of how liquid fuel transported into the cylinder of a port-fuel-injected gasoline-fueled SI engine contributes to hydrocarbon (HC) emissions. To simulate the liquid fuel flow from the valve seat region into the cylinder, a specially designed fuel probe was developed and used to inject controlled amounts of liquid fuel onto the port wall close to the valve seat. By operating the engine on pre-vaporized Indolene, and injecting a small amount of liquid fuel close to the valve seat while the intake valve was open, we examined the effects of liquid fuel entering the cylinder at different circumferential locations around the valve seat. Similar experiments were also carried out with closed valve injection of liquid fuel at the valve seat to assess the effects of residual blowback, and of evaporation from the intake valve and port surfaces.

The amount and location of liquid fuel entering the cylinder was found to have a significant impact on engine-out hydrocarbon emissions. Around the intake valve seat periphery, liquid fuel delivered closest to the exhaust valve resulted in the highest engine-out HC's, while delivery farthest from the exhaust valve had the lowest HC's. Closed valve (CV) probe liquid fuel injection resulted in lower engine-out HC emissions than did the same amount of liquid fuel with open-valve (OV) injection. This difference between OV and CV probe fuel injection was about equal in magnitude for all probe locations, indicating that the blowback during valve overlap has a similar impact on fuel redistribution and vaporization at all circumferential locations. Overall, liquid fuel flow into the cylinder produces 3 to 7 times more HC emissions per unit mass of fuel than does vapor fuel flow, depending of flow location.