Study On Spray And Spray Impingement Characteristics Of GDI Injector Based On Constant Volume Test System

As people pay more and more attention on environmental protection,energy-saving and emission reduction,the market share of cars equipped with direct injection engines is increasing.The main reason for this is that GDI technology can better control the fuel consumption of the engine and reduce the emissions of unburned hydrocarbons.The reason for this advantage is that the control of the GDI injector can precisely control the fuel injection amount and the injection timing,thereby improving the mixing mode of the mixture and improving the combustion state in the cylinder.The evaporation and atomization process of the fuel injected by the GDI injector will directly affect the formation of the mixture.Therefore,the spray characteristics and spray impingement characteristics of the GDI injector will be studied in this paper.In this paper,a spray wall impingement testing system has been designed,which volume is constant and based on GDI injectors.The system mainly includes the entire container,high-speed camera system,fuel injection system,back pressure regulation system,temperature regulation system,and wall impingement parameter adjustment system.In this article,we conduct experiments through a self-designed experimental platform.The experimental content mainly includes the influence of different factors on the spray characteristics and spray impingement characteristics.At the same time using Matlab software to compile image processing program to process the spray images taken during the experiment,and then obtaining the characteristic parameters,such as spray penetration distance,spray cone angle,spray area,hitting wall spray height,and hitting wall spray radius.We will analyze the effect of different factors on the entire evaporative atomization process of the fuel injected by the GDI injector and summarize the mechanism of influence.In the experiment,we tested the spray characteristics with different injection pulse widths,injection pressures,ambient pressures,and ambient temperatures.The conclusions obtained are as follows.When the injection pulse width is 0.2ms,0.5ms,1ms,2ms,it can be seen that the pulse width of injection is linear with the injection volume,the distance of spray penetration and the injection pulse width has no effect on the spraying speed and spray cone angle.When the injection pressure is 3 MPa,5 MPa,7 MPa,and 9 MPa,the increase of the injection pressure will lead to an increase in the amount of fuel,a faster spraying speed,an increase in the spray penetration distance,a larger spray cone angle.When the ambient pressure is 0.1 MPa,0.3 MPa,0.5 MPa,and 1 MPa,increasing the ambient pressure will result in slower spraying speed,smaller spray penetration distance,larger spray cone angle.When the ambient temperature is 20°C,40°C,60°C,80°C,increasing the ambient temperature will result in faster fuel atomization and shorter spray penetration distances.Spray cone angle will increase with the increase of ambient temperature and then decrease.In order to explore the spray impinging process,a special metal plate with the same surface roughness as the piston surface was used in the spray impinging test.After that,spray wall impinging tests were conducted under the conditions of different wall roughness,wall distance,wall inclination,ambient temperature,injection pressure,and ambient pressure.The conclusions obtained are as follows:In the first part,the roughnesses are Ra0.8 and Ra1.6,other influencing factors are fixed.From the vertical spray impinging test results,it can be known that reducing the wall roughness is beneficial to the secondary atomization of the wall-impingement spray.And There will be less spray deposited on the wall.When the wall distance from injecter in the experiment is 20 mm,30mm,40 mm,and 50 mm,it can be known that appropriate shortening of the wall distance will cause the impinging spray to rebound with higher energy and reduce the deposition of spray on the wall surface.When the wall inclination angles are 0°,15°,30°,and 45°,respectively,increasing the wall inclination angle can increase the diffusion area of the impinging spray and reduce the momentum loss caused by the impact of fuel oil on the wall surface.The spray wall collision characteristics test conducted by the same conditions as the spray characteristics test,the conclustion shows that raising the ambient temperature,increasing the injection pressure,and reducing the ambient pressure all contribute to increasing the height of the impinging spray and increasing the radius of the impinging spray.At the same time,it promotes the secondary atomization of fuel after the spray impingement and reduces the formation of fuel film on the wall,thereby improving the combustion state of the GDI engine and reducing emissions.