Measurement and Modeling on Wall Wetted Fuel Film Profile and Mixture Preparation in Intake Port of SI Engine

In SI engines with port injection system, the injected fuel spray adheres surely on the port wall and the inlet valve, consequently, the spray-wall interaction process leads to the generation of unburned hydrocarbons and uncontrollable mixture formation. This paper deals with the fuel mixture preparation process including basic research on characteristics of the wall-wetted fuel film on a flat wall inside a constant volume vessel. In the experiments, iso-octane mixed with biacetyl as a tracer dopant was injected through a pintle type injector against a flat glass wall under the ambient conditions of atmospheric pressure and room temperature. The thickness of the adhered fuel film on the wall was quantitatively measured by using laser induced fluorescence (LIF) technique, which provides 2-D distribution information with high special resolution as a function of the injection duration, the impingement distance from the injector to the wall, and the impingement angle against the wall. Further more, a spray-wall interaction submodel including the fuel film formation proposed by the authors in previous work, was modified for application to SI engines. In this submodel, fuel film formation due to the droplet-droplet interaction near the wall and droplet-wall film interaction, fuel film transport, droplet interaction film breakup, and the velocity and direction of dispersing / splashing droplets were considered based on several experimental results. This spray-wall interaction submodel was incorporated into KIVA-II code [1]. Then, the fuel film profile formed on the wall and the mixture preparation properties such as the evaporated fuel vapor and non-evaporated liquid phase droplets were calculated and compared with experimental results.