Simulation Research On Particulate Matter Emissions Of Gasoline Engine Combined Port Fuel Injection With Direct Injection

Recently, nationwide hazy weather draws more attention to the particulate matter withinthe atmosphere, while the prime fraction of GDI engine is nuclear particles which are moreharmful to the environment and people’s health. So domestic and overseas regulations havebeen confirmed specific limitations to the GDI engine. According to some reports, gasolineengines which combined port fuel injection with direct injection have great influence ondecreasing the PM emissions. So the author has used the three-dimensional simulationsoftware AVL-Fire to investigate the influence of this combined strategy to the sootemissions which are the most part in the PM emissions. During the research, here comesthese conclusions:(1)Within ideal air-fuel ratio, the simulation research of mixture formation, cylindercombustion and soot emissions within three different injection strategies which are directinjection, mainly port fuel injection and mainly direct injection has been made. Theconclusion shows, injection strategy has little influence on the average temperature and theaverage pressure of the cylinder, but has a greater effect on the final soot emissions. Withinthree different injection strategies, mainly port fuel injection has the least number in the sootconcentration and mass fraction, while the direct injection has the largest soot emissions.Mainly port fuel injection has obvious advantage in soot emissions, which decreases3-5orders of magnitude in mass fraction than direct injection while decreases1-3orders ofmagnitude in soot number concentration.(2)Researching the influence about different fuel injection proportions in mainly portfuel injection strategy, different fuel injection proportions affect the homogeneity of themixture which is the main formation reason of the soot emissions. The number concentrationof soot is determined by the overrich region. When port fuel injection proportion arrives acertain value, the decreasing trend of soot mass fraction and number concentration is weakened. Comprehensively, the optimized fuel injection strategy under mainly port fuelinjection is80%port fuel injection and20%direct injection.(3)Under the best strategy of the mainly port fuel injection situation, the PM emissionsinfluence of the injection timing and injection duration about the combined gasoline enginehas been investigated. As the conclusion shows, the influence of injection timing andinjection duration on mean temperature, mean pressure and heat release rate is small, whilethey are sensitive to the soot mass fraction and number concentration. The early or lateinjection timing will cause the increase of the soot emissions. When the injection timing islate, the final soot emissions will be1order of magnitude higher than the early timing. Sothe best injection timing is320°CA BTDC under simulation situation. The long and shortinjection duration will increase the soot emissions, while the injection duration is short theinfluence is larger than the injection duration is too long. When the injection duration is short,the final soot emissions will increase two orders of magnitude in mass fraction than theduration is long, while increase1order of magnitude in number concentration. Under thesimulation situation, the best injection duration is about8°CA.