Abstract: The cavitation and fuel atomization characteristics of an ultra-high pressure fuel injector in a certain diesel engine were investigated through Computational Fluid Dynamics (CFD) fluid simulation. On the basis of verifying the diesel fluid grid,the effects of nozzle diameter,nozzle inlet roundness radius,and nozzle angle on the diesel gas phase flow field were analyzed,and the average diesel gas phase fraction and atomization effect at the nozzle outlet were studied. The results show that the diameter of the nozzle,the radius of the chamfer,and the angle all significantly affect the diesel atomization characteristics. As the diameter of the nozzle increases,cavitation phenomenon shifts from the bottom to the top,and the average diesel gas phase fraction first increases and then decreases;increasing the radius of rounding reduces cavitation intensity and average diesel gas phase fraction,but improves flow performance;the increase in angle causes cavitation to transfer from the lower wall to the upper wall,resulting in an increase in average diesel gas phase fraction and improved atomization effect. Through orthogonal simulation experiments,the optimized parameter combinations were obtained as nozzle diameter of 0.26 mm,rounding radius of 0.02 mm,and angle of 90°,the diesel flow rate at the nozzle outlet was 189.3 mL/s,and the average diesel gas phase fraction was 25.6 %. Finally,the accuracy of the simulation model was verified through experiments,and the optimized fuel injector has excellent atomization effect and flow characteristics.

Key words: Computational Fluid Dynamics(CFD), ultra-high pressure, injector nozzle, cavitation, orthogonal test