Macroscopic and Microscopic Spray Characteristics of Diesel and Gasoline in a Constant Volume Chamber

Abstract

The aim of this study is to investigate the spray characteristics of diesel and gasoline under various ambient conditions. Ambient conditions were simulated, ranging from atmospheric conditions to high pressure and temperature conditions such as those inside a combustion chamber of an internal combustion engine. Spray tip penetration and spray cross-sectional area were calculated in liquid and vapor spray development. In addition, initial spray development and end of injection near nozzle were visualized microscopically, to study spray atomization characteristics. Three injection pressures of 50 MPa, 100 MPa, and 150 MPa were tested. The ambient temperature was varied from 300 K to 950 K, and the ambient density was maintained between 1 kg/m3 and 20 kg/m3. Gasoline and diesel exhibited similar liquid penetration and spray cross-sectional area at every ambient density condition under non-evaporation. As the ambient temperature increased, liquid penetration length and spray area of both fuels’ spray were shortened and decreased by fuel evaporation near the spray boundary. However, the two fuels were characterized by different slopes in the decrement trend of spray area as the ambient temperature increased. The decrement slope trend coincided considerably with the distillation curve characteristics of the two fuels. Vapor spray boundary of gasoline and diesel was particularly similar, despite the different amount of fuel evaporation. It was assumed that the outer spray boundary of gasoline and diesel is always similar when using the same injector and injection conditions. In microscopic spray visualization, gasoline spray displayed a more unstable and asymmetric spray shape, with more dispersed and distributed fuel ligaments during initial spray development. Large amounts of fuel vapor cloud were observed near the nozzle at the end of the injection process with gasoline. Some amounts of this vapor cloud were attributed to the evaporation of residual fuel in the nozzle sac.