During cold operation period, fuel injection system directly contributes the unburned hydrocarbon formation in spark ignition engines. The relationship between injection parameters and HC emission behavior was investigated through a series of experiments. Spray behavior of port fuel injectors was macroscopically characterized at first, followed by a quantitative evaluation of mass concentration of liquid fuel by a patternator and microscopic measurements. Dual-hole injector was found to produce finer spray than single hole one. Using a purpose-built test rig, the wall wetting phenomena were investigated with various parameters such as wall and fuel temperatures, wall roughness, amount of fuel, distance and angle of the injection relative to the wall. The amount of wetted fuel was mostly affected by wall temperature.
Varying coolant temperature(20∼80℃), HC emissions were also measured by a fast-response flame ionization detector(FR-FID) and NDIR(Non-dispersive Infra-Red Analyzer) in a production engine. Wetting plate temperature and angle were found to be the most influential factors to wetting amount. Little effects were brought out either by varing fuel temperature(30∼140℃) or plate roughness and in more higher fuel temperaure region than 140℃ wetting fuel amount had got to be nearly disappeared which is caused by flash boiling. Colder engine produced more wetting fuel and consequently generated more HC emissions. With respect to the different types of injectors, HC emission was also measured. In the Dual-hole injector application, though it has the advantages of finer atomization quality, the degradation of targeting had much more adverse effect. The control schemes to reduce HC emissions during cold start could be suggested from the findings that the amount of fuel supply and HC emission could be reduced by utilizing fine spray and high intake wall temperature.
