Study On The Spray Characteristics Of Methanol DI Engine

Energy shortages and environmental crises are serious problems facing human society,finding clean and efficient alternative flues is one of the priorites of engine researchers.High-quality alternative flues can minimize engine fuel consumption and pollutant emission while ensure adequate engine performance.Among the alternative fuel that have been developed,methanol has received widespread attention due to its great power performance an,low pollutant emission and wealth of sources.In this paper,the characteristics of high pressure direct spray on methanol were studied by combining experimental and CFD methods.,completed methanol high-pressure inject experiment on a constant volume chamber,investigated the effects of inject conditions and environment on methanol spray.Through carrying out numerical simulation on a DI engine model,this paper compared the influence of different inject pressure and strategies on spray and mixture formation process.Conclusions are as below:(1)The methanol spray penetration increases nonlinearly as the injection pressure increases,and the influence of the injection pressure on the penetration distance decreases as the injection pressure increases.Ambient temperature affects the spray penetration by affecting the evaporation rate of methanol.The high pressure spray cone angle of methanol is greatly affected by environmental conditions(temperature,pressure),and not sensitive to the changes in inject pressure.(2)The development process of methanol direct spray in cylinder could be divided into three processes:the free development of spray,the separation of air after spray hits the wall,the disappearance of spray partition.High inject pressure could reduce the time for the spray to separate air,so that the evaporation rate of methanol and uniformity of mixture can both increase.(3)If spray expansion angle ? is too great,spray would hit the cylinder wall and a large amount of film would be formed on the surface of cylinder wall.The reduction of ? could effectively reduce the amount of film.If ? is too small,the spray will be so tense that the mixture concentration is uneven.It's necessary to weigh both the film amount and mixture uniformity when setting spray expansion angle ?.(4)Increasing the number of nozzle holes can significantly reduce the amount of liquid film in the cylinder.With the increase of the number of orifices,the maximum evaporation rate of methanol and the uniformity of mixture concentration increase first and then decrease.(5)The proper two-stage-injection strategy could effectively reduce the amount of film produced in cylinder,however,it will also reduce the uniformity of mixture concentration.The uniformity of the mixture concentration increases with the delay of the second injection timing,and decreases with the proportion of the second injection methanol increases.There are optimum second injection timing and injection ratio would minimize the amount of film.(6)Before the top dead center,the higher the methanol concentration in a certain area,the lower the temperature of the area;the more uniform the methanol concentration distribution,the more uniform the temperature distribution.