Development of Fan Spray Simulation for Gasoline Direct Injection Engines

In gasoline direct injection engines it is important to optimize fuel spray characteristics, which strongly affect stratified combustion process. Spray simulation is anticipated as a tool for optimizing nozzle design, but conventional simulation, which is based on experimental data and/or empirical laws regarding spray boundary condition at the nozzle exit, cannot predict the effect of various nozzle geometries on spray characteristics. In Japan, a fan spray injected from a slit type nozzle has recently been adopted for gasoline direct injection engines. This paper proposes a computational model for the fan spray. The structure of two-phase flow inside the nozzle is numerically analyzed using the volume of fluid (VOF) method in a three-dimensional CFD code based on the nozzle geometry. The results of these analyses are applied to classical linear instability theory to calculate fuel droplet mean diameter after primary breakup. These results lead the boundary condition at the nozzle exit for the spray simulation instead of experimental data and/or empirical laws. The conventional discrete droplet model (DDM) and many sub-models are used for spray calculation. Spray tip penetration, Sauter mean diameter (SMD), and spray mass flow distribution are verified for various atmospheric pressures and nozzle geometries.