Investigation Of Impinging Spray And Film Movement And Breakup Characteristic Based On Optical Diagnostics

With the increasingly strict environmental regulations,the gasoline direct injection engine has been widely used due to its low fuel consumption,high power and high compression ratio.However,the high pressurization and miniaturization of the engines cause the inevitable spray impingement problem.The fuel is in contact with the top of the piston and the cylinder wall to form an oil film that is difficult to vaporize and be burned,most of which is discharged into air in the form of soot,affecting the power output and discharge performance of the engine.This problem is especially noticeable under cold start conditions.Therefore,research of the spray impingement is of great significance for improving the performance of the engine.Based on a variety of optical diagnostic methods,this study has carried out in-depth and systematic research on the spray impingement and corresponding film.A single droplet generation system with different diameters and impinging velocities is developed.The macroscopic structure and film dynamics of single droplet impingement are measured by micro-backlight imaging and micro-laser induced fluorescence.Then the influence of different Weber numbers on single droplet and wall interaction is analyzed.The distribution of particle size and velocity of droplets near the wall of single-plume spray are obtained by Phase Doppler Interference and particle image velocimetry.By analyzing the glided away phenomenon of single droplets near wall surface,the traditional Bai & Gosman spray impingement model is further improved.The movement and mass distribution of film under different thermodynamic states are measured by laser induced fluorescence technology.The waves above the film could be divided into three types depending on the generation rules,spreading speed and thickness distribution in the center line.The mass detachment caused by wave breakup under different plate temperature and fuel temperature are further calculated and compared.The macroscopic structure of impinging spray and development and breakup dynamics of film are fully investigated in this study,and the mechanism of single droplet impingement near the wall is improved.The results provide a solid foundation to improve the emission performance of engine and accuracy of simulation models.