Analysis on Simulation Characteristics of Diesel Sprays with Discrete Droplet Model

Abstract

This paper investigates the simulation characteristics of diesel sprays with DDM (Discrete Droplet Model), which is commonly used in engine combustion simulations. In this study KIVA-II code, which was developed in Los Alamos National Laboratory in the United States and it is one of the most popular simulation programs for diesel combustion, was used for the analysis. With making the evaporation speed and the droplet diameter agree with experiments, the penetration of fuel vapor was investigated, as it is closely related to the air-entrainment in the fuel spray. Comparisons were made for mesh sizes, turbulence factors, and drag coefficient of the droplets. The results show that the non evaporating spray can be simulated well by adjusting the parameters, but the evaporating spray is hardly simulated well by the adjustment. It strongly depends on mesh sizes and almost infinitesimal mesh is required particularly at the vicinity of the nozzle exit. A method to have good simulation results for the evaporating sprays with the coarse mesh is demonstrated in the paper, but further investigation is necessary for the appropriate simulation of combusting sprays.