Variation of Sauter Mean Diameter of Droplets of Gasoline Engine Intake Port during Cold Start

Abstract

The reduction of sauter mean diameter (SMD) of droplets means the percent of the evaporated fuel, which is important to the formation of the combustible mixture in a port-injection gasoline engine during cold-start. Three-dimensional numerical simulation of SMD of the droplets in the inlet port of a gasoline engine was employed using the CFD software. This paper presented the effect of multi-parameters on SMD of the droplets including initial droplet velocity, intake temperature, fuel temperature, injection timing and engine speed. The simulation results show that the most influential parameters on SMD of the droplets are intake temperature and fuel temperature. The fuel evaporation rates increase approximately linearly with the intake air temperature and fuel temperature increasing. The initial droplet velocity and injection timing have a little effect on the fuel evaporation. As engine speed increases, SMD of the droplets firstly decreases and then increases. After intake-valve-open (IVO), back flow of gas in cylinders results in steep reduction of droplet diameter.