Computational Study of the Air/Fuel Mixture in a Small Spark Ignition Engine

In an effort to understand the fluid dynamics in the droplet formation process, during the fuel delivery portion of operation of a small spark ignition engine, a computational study of the process was undertaken. A combination of high-speed photography and Computational Fluid Dynamics was used to investigate the droplet formation process. Droplets of liquid are stripped from a column of liquid and entrained in a high velocity, cross-flow air stream. This process is known as aerodynamic stripping. This aerodynamic stripping is the process by which fuel is metered and delivered to a spark ignition engine. The condition of the fuel and air mixtures has an impact on the combustion event in the engine. Therefore, a thorough understanding of the fuel delivery process is desirable. This paper details a comprehensive CFD model that was created to explore the possibility of modeling the droplet breakup process. The mesh density required for this analysis was investigated. The accuracy of the predictions was verified by comparing the CFD results with high-speed film taken of the process. The results show that the process can be modeled accurately, provided the correct size mesh is used, and that the predicted droplets compare well with those seen in the film.