Study On Spray Impingement And Combustion Characteristics Of Diesel Fuel In Constant Volume Combustion Chamber

China has a vast territory,of which the plateau region is widely distributed.In recent years,the use of diesel engines in highland areas has increased.When the diesel engine is operating in the plateau area,the air intake density is reduced,then the spray penetration increases,which can easily lead to spray hitting the wall or even the liquid fuel wet wall,resulting in diesel engine power drop,fuel consumption increase,heat load increase and emissions deteriorated during the work process.According to the above situation,it is of great significance to study the spray impingement characteristics and analyze its impact mechanism on the spray combustion process.In this paper,using the constant volume combustion chamber test platform,a pre-mixed combustion method is used to construct a similar thermal environment near the top dead center of a diesel engine.The process of fuel spray is captured by various optical measurement methods.The characteristic parameters concerned in different processes were measured and analyzed using corresponding image processing methods,to explore the influence of the impingement of the fuel spray on the combustion process.Firstly,according to the main operating parameters of the vehicle diesel engine,six representative altitude conditions from 0 to 4500 m are selected to investigate the spray liquid phase penetration and ignition characteristics of the fuel spray at different altitudes.The results show that when the altitude rises to 3000m,there is a clear liquid-phase fuel wet wall phenomenon during the spray process,and the ignition delay is greatly extended.And at the altitude of 4500m,the first combustion point is close to the wall surface,and the phenomenon of wall-burning is observed.Then,from the two aspects of changing the thermal environment and the fuel injection strategy,the conditions indifferent degree of wall-wetness were obtained by changing the two parameters of the charged density and the diameter of the nozzle hole.Charging density range of 7.5~15kg/m~3and nozzle diameter of 0.11~0.22mm were selected.The results show that the decrease in the charging density will lead to an extension of the ignition delay period,and the period will be further delayed as the wetness degree increases.Meanwhile,the spray ignition point is located in the spray diffusion area on the wall,the duration of combustion is shortened,the heat release rate is increased,and the emission of soot increases.However,in the experimental conditions,which of high temperature,fuel injection pressure and inflation density,the change of nozzle diameter has no significant effect on the ignition delay,and also the delay is not affected by the degree of wall-wetness.In addition,during the combustion process,the soot generation and oxidation rate increase with the increase of the nozzle diameter,and the soot emission does not change obviously with the wetness degree increases,but the radial penetration distance of the impinging flame increases.Under the condition of same injection rate,the afterburning phenomenon is serious with the degree of wall-wetness increases,the production of soot in the spray combustion process increases rapidly,and the soot residue after combustion is also increased.