Effects of injection parameters on the amount of wall-wet fuel in a port-fuel-injected spark-ignition engine during cold start.

In a four-stroke cycle port-fuel-injected spark-ignition engine, a significant portion of unburned hydrocarbons is exhausted during the short period of cold start. The aim of this study is to investigate the physics behind the wall-wet phenomena and its determining parameter as simply as possible even though qualitative to some extent. The test engine is driven at a constant speed of 350 r/min. The fuel injection starts at a certain cycle, and the cycles required for the first ignition is counted. Three gasoline injectors having different atomization characteristics are used for port fuel injection, and the droplet size, the spray angle and the spray velocity are varied independently. The fuel transport phenomena from the injector to the cylinder are characterized by only two parameters, α and β, the mass fraction of the fuel without wall-wet and the mass fraction of the evaporated fuel from liquid films on walls. They are determined so that all the first ignition cycles observed experimentally are consistently reproduced by the model. The value of α is successfully determined for every single injector, and it increases monotonously with the decrease in the Stokes number. [ABSTRACT FROM AUTHOR]