Numerical and Experimental Analyses of Mixture Formation Process Using a Fan-shaped DI Gasoline Spray: Examinations on Effects of Crosswind and Wall Impingement

The analysis of spray characteristics is important to examine the combustion characteristics of DI (Direct Injection) gasoline engines because the fuel-air mixture formation is controlled by spray characteristics and in-cylinder gas motion. However, the mixture formation process has not been well clarified yet. In this study, the characteristics of a fan-shaped spray caused from a slit-type injector, such as the droplet size, its velocity and the droplet distribution were simultaneously measured on a 2D plane by using improved ILIDS (Interferometric Laser Imaging for Droplet Sizing) method. ILIDS method is an optical measurement technique using interference fringes by illuminating a transparent spherical particles with a coherent laser light. In the measurement of the wall-impinging spray, effects of the distance to the wall and the wall temperature on the spray characteristics were investigated. As a result, it was found that the SMD (Sauter Mean Diameter) near the wall surface increased with smaller distance. Meanwhile, in the measurement of spray under a crosswind, the relative velocity of between the droplet and the ambient gas was found influential on the atomization. Additionally, numerical simulation of the spray with a crosswind was examined. The in-nozzle two phase flow was calculated using VOF (Volume of Fluid) model and also the spray formation process was calculated using DDM (Discrete Droplet Model) with mathematical sub-models.

As a result, the effects of boundary conditions at nozzle exit, breakup model and drag force model were evaluated comparing with experimental results.