Experimental Investigation On The Characteristics Of GDI Spray Impinging On The High Temperature Wall Surface

Compared with the traditional port fuel injection engine,the gasoline direct injection engine has been applied more and more widely due to its advantages of good economy,strong power performance and quick response under variable operating conditions.However,the wall wetting phenomenon would occurred caused by the spray-wall impingement phenomenon in gasoline direct injection engine.And this wall wetting phenomenon would more serious with the development of small reinforcement of gasoline engine.The harms including the emission of particulate matter increasing,oil dilution,friction increasing,early combustion and super knock.This paper carried out a quantitative study on the wall film formed by spray-wall impingement in gasoline direct injection combined with the research status at home and abroad,aiming to improving the existing spray-wall impingement model by providing more experimental data.This paper carried out a quantitative study on the wall film formed by spray-wall impingement in gasoline direct injection engine,using laser-induced fluorescence technologies.Results show that the mass of fuel film is 4.07 mg,when the wall temperature 293 K,64.4% of the total mass of a single injection.The mass of fuel film would decrease with the rise of wall temperature.At the same time,it was found that the Leidenfrost effect inhibited the continuous decrease of film mass.Compared with the single droplet impingement,the retention time of wall droplets in spray impingement is shorter,due to the interaction of numerous droplets.Unlike the film mass,the film area increases with the increase of wall temperature,when the wall temperature is below 373 K.Compare with the single injection,the mass of fuel film formed by spray-wall impingement decreases using double injection strategy,provided that the total injection mass is the same.And film mass further decreases with the extension of injection interval time.It is found that injection interval time have a great influence on the film mass.The development trend of film mass is that growth rate slower in the early stage,faster in the middle stage and slower in the late stage.The development trend of the film area is that grows rapidly in the early stage of spray impingement,then it grows at a slower rate.The near-field microscopic characteristics of spray impingement show that crushing phenomenon have been occurred with the increase of wall temperature,and this phenomenon would be aggravated with the rise of the wall temperature,leading to smaller droplets.The difference between droplet impingement and spray impingement is that the survival time of wall droplet formed by droplet impingement is longer than that of spray impingement,because the interaction between droplets was not considered in droplet impingement.Crushing phenomenon can occur further away from the spray center with the increase of wall temperature.The Leidenfrost effect inhibits the breaking process of the impinging droplets.