## 1 Introduction  
Light weight, high thermal efficiency, wide power range and compact structure is the characteristic of diesel engine. With vehicle weight reduction, the volume of the diesel engine has been reduced gradually in recent years, resulting in the spray penetration was short and the phenomenon of diesel spray came into collision with piston or cylinder wall occurring during fuel injection. After spray hitting the wall, the spray radius and height is changed, which will affect the mixing of fuel and air, and further affect the engine performance and exhaust particulate emissions. Therefore, it is significant to study the phenomenon of spray impingement on diesel engine [1; 2; 3; 4; 5].  
The researches on spray characteristics were mainly based on the environmental density, the oil injection pressure and the angle of collision. Environmental density refers to the quality of unit volume air under certain temperature and pressure. [PERSON] et al. [6; 7] studied the characteristics of diesel spray wall collision by quantitative analysis. Put forward the conclusions that spray radius decreases and spray height increases with the increase of environmental density. [PERSON] et al. [8] studied the characteristics of diesel spray with high injection pressure by numerical simulation. Posed the conclusions that little effect on the volume of diesel spray and entrainment air quality but great effect on crushing rate by the injection pressure at low back pressure. [PERSON] et al. [9] studied the effect of injection pressure on the spray characteristics of diesel by experiment. It was concluded that the effect of injection pressure on the liquid phase spray cone angle was minimal and the higher injection pressure caused higher vapor phase spray penetration rate. [PERSON] et al. [10] conductedexperiments, went into the effects of ambient density, injection pressure and impact angle on the flow characteristics of impinging diesel spray. They concluded that the average peak velocity was positively correlated with the spray center velocity. [PERSON] et al. [11] studied the effect of nozzle inclination angle on spray characteristics by experiments and concluded that the lower angle of inlet hole was favorable for faster jet penetration. [PERSON] et al. [12] did experimental research, investigated on the effect of shock wave, it was found that shock waves have a positive effect on nozzle penetration and air quality. However, they inhibit the radial development of spray. The researchers not only studied the spray characteristics of biodiesel, but also analyzed the spray characteristics of methanol diesel. [PERSON] et al. [13] compared the characteristics of diesel and biodiesel by theoretical and experimental comparison, concluded that the cone angle of diesel was wider than biodiesel and the penetration time of diesel tip was shorter than biodiesel at the same injection pressure. [PERSON] et al. [14] made comparison with the spray characteristics of methanol-diesel and diesel, the results showed that diesel has more symmetrical spray shape and thinner spray boundary.  
Researchers considered the influence of all aspects on the spray characteristics, and reached a remarkable depth by experiments and simulations. However, in the process of diesel spray impingement, many of researchers obtained experimental data that was not detailed enough. In this paper, firstly the visualization experiment system, its working process using constant volume combustion bomb and high-speed camera is introduced. The spray images are obtained by using the scattered light of small droplets. Secondly the grid division, model selection and parameter setting is given by using numerical simulation software (converge). The experiments and simulations of diesel spray impingement are carried out. The variation of spray radius and spray height in the process of diesel spray impingement is analyzed and the accuracy of the simulation is proved.