Emissions and Fuel Utilisation After Cold Starting Spark Ignition Engines 1999-01-0220

A model has been developed to interpret experimental results for emissions and air/fuel ratio variations recorded during warm-up from cold starts at temperatures down to -20°C. The model describes fuel transport and utilisation after injection to its exhaust as fuel products or loss to the crankcase, and allows for the storage of fuel in films on the intake port surface, in-cylinder surfaces and in the piston “crevice”. Engine-out emissions of unburned hydrocarbons are treated as being comprised of contributions from the bulk charge, fuel returning from in-cylinder wetted surfaces and from fuel stored in the piston crevices. The model characterises engine-out emissions and air/fuel ratio variations successfully under both quasi-steady and transient engine operating conditions during warm-up. Good agreement between experimental data and model predictions has been achieved for a wide range of engine operating conditions. The model equations set has been derived from phenomenological arguments. Despite the complexity of the processes described, empirical constants/functions depend on engine coolant temperature only. The model has been used to investigate implied variations of in-cylinder fuel film mass, fuel loss to the crankcase, exhaust air/fuel ratio variations and engine-out emissions.