Study On The Characteristics Of Spray And PM Exhaust For A GDI Engine

Gasoline direct injection(GDI)has become a mainstream technology in automobile power-train as its excellent advantages in power performance,fuel economy and emissions.In recent years,with particulate matter(PM)concepts into public view,automobile exhaust and environmental protection has been given more attention.Compared with the traditional port fuel injection(PFI),GDI engine as its inadequate-mixing characteristics of PM emissions performance is poor.Not only the limit of mass particles but also the limit of number has carry out in the latest European emission regulations on GDI engine,what brings great challenges.Based on the simulation platform,a CFD analysis on the characteristics of exhaust of PM was been researched on a 1.6L GDI engine.The mixture formation process,mass of wall fuel films and PM emissions in cylinder were been improved through optimizing fuel injection strategy.The main results and conclusions obtained are as follows:(1)According to the engine test,simulation platform of GDI engine was build with STAR-CD.The ECFM-3Z combustion model was calibrate through adjusting the ?,?parameters and initial flame kernel radius.The calibration result shows that the simulation results are matched with performance experiment.The droplet break-up and particle-wall interaction of spray model was calibrate based on a visual spray test.The results show that spray configuration and angle and Sauter mean diameter(SMD)consistent with the test,and errors within a reasonable range.(2)From the perspective of in-cylinder PM emission,the study on optimization of fuel injection strategy was researched based on the model which had been calibrated before.The results show that formation of particulate matter is closely related to the in-cylinder gas mixing and mass of wall films.(3)Compared with single injection strategy,injection twice a cycle can facilitate the quality of fuel-gas mixing,reduce the wall films,and improve the PM emission performance obviously.In-cylinder PM mass fraction show a trend from decline to rise while second fuel distribution proportion increasing.The best injection percentage is65%:35%.(4)Wall films and PM emission will be deteriorated when fuel injecting both early or late.Start of injection when 283.5°CA BTDC under single injection strategy,In-cylinder film and PM emission are optimum,and PM mass fraction show a trend from rise to decline while injection was delayed.(5)For the situation of two stage injection,the best SOI2 is140°CA BTDC.PM mass fraction show a trend from decline to rise while injection shift to an earlier.