Experimental Study On The Impact Characteristics Of Single Fuel Droplet On The Wall And Its Influencing Factors

The study of single droplet impinging on the wall is the foundation of the spray impinging on the wall.The research on the motion characteristics of single liquid droplet hitting wall and its interaction with wall surface can extend and improve the mechanism of the whole spray hitting wall.Based on the latest research progress in internal combustion engine combustion,the basic scientific research was carried out on the impact behavior of fuel droplet on piston top surface and cylinder liner wall surface with the oil film.This paper built a backlight method of single droplet test system and a laser induced fluorescence single droplet test system.The dynamic process of a single droplet hitting the wall was photographed from multiple angles with a high-speed camera.The movement patterns and parameters of fuel droplet hitting the wall under different impact conditions were studied.Relevant conclusions of this paper are as follows:After the fuel droplet hit the solid dry wall with a wide and large Weber number,a fuel film attached to the wall is formed.The spread diameter of the fuel film increases with the increase of the initial velocity and diameter.At the same Weber number,the maximum spread factor of the attached fuel film does not change with the initial velocity and diameter.The maximum spreading factor is related to Weber number,independent of initial velocity and initial diameter.The attached fuel film changes the dry and wet state of the wall.The existence of attached fuel film is an important reason for the subsequent liquid droplets to hit the wall and cause the coronal liquid film and splash phenomenon.The thinner the fuel film attached to the wall,the more violent the liquid droplets splash.The fuel droplet impinged on the liquid film of wide and high viscosity under the conditions of wide and large Weber numbers,forming a bowl of liquid film and entering the wall liquid film along with the bowl of liquid film,diluting the liquid film.The shape of the bowl-shaped liquid film is greatly affected by the thickness of the liquid film on the wall and less affected by the viscosity of the liquid film on the wall.The larger Weber number and the thinner liquid film are beneficial to the formation of larger bowl top diameter.With the continuous impact on the wall,the dilution ratio of the liquid film on the wall increases,and the form of the impact gradually changes from the bowl-shaped liquid film to the coronal liquid film.The splash degree increases with the increase of the dilution ratio,and the splash droplets contained oil film on the wall.The difference of viscosity of droplet has little effect on the phenomenon of droplet impinging on the liquid film with low viscosity,but great influence on the phenomenon of droplet impinging on the liquid film with high viscosity.Low viscosity liquid droplet impact on high viscosity liquid film will form a circular liquid ring,not easy to spatter.Once the liquid droplet hit the liquid film,the components of the liquid droplets come from the liquid film and the liquid droplet.The proportion of spatter droplets is mainly related to the thickness of wall liquid film,but not to its viscosity.When the thickness of wall liquid film increases,the proportion of wall liquid film in the splash droplets increases.