Numerical Study Of Spray Impingement And Wall-Film Evaporation In The Combustion Engine

The phenomenon of spray impingement and wall film will occur inevitably in the combustion engine. Because of the low injection pressure and wall temperature at cold start in port fuel injection gasoline engine, the spray will not atomize adequately and caused liquid fuel film deposition on the port wall and back of inlet valve. For the gasoline direct injection engine of small cylinder bore, the distance between nozzle and piston wall is short and there are little time for the spray and air to mix uniformly. So the fuel film is likely to adhere on the piston wall cylinder liner. These unevaporated wall film not only influence the formation of gas mixture, but also lead to the addition of unburned hydrocarbons.With the rapid development of CFD fluid simulation software, the multidimensional numerical simulation for the working process of engine has come true, and it is possible to explore the complex turbulent motion in cylinder. In this paper, the Discrete Phase Model (DPM) in the FLUENT which is based on the Euler-Lagrange method is used. With this method, the spray impingement and wall film evaporation model is established, and the influence factors of film evaporation are studied. The main contents of this paper are as follows:Firstly, the single hole spray impingement and wall film evaporation model for low injection pressure is established according to the experimental conditions in literature. The simulation results of film thickness and film area are compared to experimental data and have a good agreement. The deviation between simulation and experiment is small. And then some factors that influence film evaporation are studied, such as, injection height, injection duration, injection angle, injection pressure, wall temperature and air flow. The change laws of wall film mass ratio and fuel vapor mass ratio are summarized.Secondly, the multihole spray at the condition of gasoline direct injection is studied, the process of wall film formation and evaporation are analyzed. A constant volume model is set up based on the experimental conditions in the literature and the spray penetration and morphology are consistent with experiment results. The influences of injection pressure, wall temperature and ambient pressure on the film evaporation are analyzed.Finally, the wall mesh movement is added into the model. The In-cylinder model in FLUENT is used for the modeling of reciprocating motion of piston wall and the spray injection at the later of compression stroke. The variations of wall film mass evaporation mass are researched through changing injection timing and pressure.Through setting up the wall film model on the conditions of gasoline engine, and analyzing the factors that influence film evaporation, the results in this paper can provide some theoretical basis for the reducing of wall film ratio and the emission of hydrocarbon.