Experimental And Simulation Study On Spray-Wall Impingement Of GDI Injector

As the development of automotive industry, the car ownership of China increased in these years and China has become one of the countries own most amount of cars. Faced with the challenge of energy and environment, gasoline direction injection(GDI) technology become more and more important in developing the power and fuel economy and has become more and more popular in auto market. However, the problems of oil dilution and soot production caused by the spray-wall impingement phenomenon seemed unavoidable. As the spray-wall impingement in GDI engine is different greatly with that in diesel engine due to different injection condition, gasoline also has different physical and chemical property with diesel, it is necessary to analyses the phenomenon of gasoline spray-wall impingement.A GDI injector of six nozzles was modified to single hole injector, based on test of the reliability of newly single hole injector, optical test system and phase Doppler analyses system were employed to analyses the spray-wall interaction with different wall condition. The spray structure of spray, droplet size distribution, characteristic particle size and normal velocity were studied. It shows that spray impinged on wall at small distance may caused different droplet size distribution and caused normal velocity changed its direction due to bounce; heated wall may promote the evaporate and bounce of droplets, changed the range of droplet size distribution, most droplets in measuring area have a velocity near 0m/s because of high temperature of the wall; spray impinged on a wet wall may greatly change the distribution of droplet size and velocity distribution range, the droplets whose velocity in the range of 10m/s-30m/s decreased compared with dry wall condition. At the same time, the impinged position play an important role in the spray-wall interaction, the difference tend to be smaller when the spray impinged on a wall at longer distance.Based on the experimental data, a 3D CFD software FIRE was used to simulate the spray-wall impingement in different wall conditions using different spray-wall interaction model. The simulation result was compared with experimental data. It shows that the Bai Gosman model has simulation accuracy in modeling the spray structure, the spray size distribution could reflect the influence of wall position and wall temperature, but the small distance impingement droplet size distribution differ from the experiment data. Mundo/Sommerfeld model simulate the droplet size in a small range and did not show the temperature difference in the droplet size distribution result, while the Kuhnke model has the same accuracy limit. The Bai Gosman model then was modified, the result shows better agreement with the experimental data, which means that the modified Bai Gosman model fits better in this spray-wall impingement condition.In conclusion, the phenomenon after spray impinging on a wall has been classified in several classic ways, but different phenomenon may be caused by different injection conditions and different wall conditions, large amount of measurement should be done and spray-wall for extensive applicability should be built to offer more guide in design of GDI engine.