Matching Research Of TGDI Gasoline Engine Combustion System On Multi-factor At Combined Working Condition

In the context of fuel-saving and emission reduction of fuel vehicles,the combustion system optimization has been an important part of gasoline engine performance.In order to improve fuel economy and emission performance and the research process of simulation of combustion system;this paper took an TGDI gasoline engine combustion system as the research object.The influence of inlet structure and fuel injection parameter was studied by CFD simulation.the engine rated operating point and the 2000 r/min@ 0.2 MPa were selected to simulate and test the effect of piston shape on the combustion system for the combined conditions of studying.Firstly,this paper screened six intake ports through airway steady-state test,and explored the effects of high flow coefficient and high tumble port on the combustion system.The simulation results show that the high tumble flow ratio intake promotes the rapid formation of high-speed ordered rolling in the cylinder,which is conducive to the uniform mixing of oil and gas and the rapid propagation of flame,but lots of fuels are carried to impact the exhaust side cylinder wall,and the accumulated maximum wall fuel amount of the liner reaches 3.54 mg,which is much higher than the high flow coefficient intake of 0.94 mg.In the research of combined working condition evaluation based on the piston crown shape,the simulation results show that the piston designed with smooth slope on the exhaust side is good under the rated working conditions in terms of mixture gas uniformity,combustion characteristics and wet wall conditions of the liner fuel and it is beneficial to the improvement of kinetic energy under both working conditions.The piston designed with high back step is good in terms of the uniformity of the mixture at 2000 r/min@ 0.2 MPa.The emission test results show that under the rated working conditions,the CO and HC emission concentrations of the piston with high back step combustion system are 38.4 % and 77.8 % higher than another respectively,while that of the piston with smooth slope combustion system are 14.5 % and 34.2 % higher than that one respectively under 2000r/min@ 0.2 MPa.These results show that with the change of working conditions,the advantage and disadvantage of the piston scheme on the tumble ratio and turbulent kinetic energy are basically unchanged,but the difference between the mixture gas uniformity,flame propagation speed and CO and HC emission characteristics is different.therefore,the combined conditions of high speed with large load and low speed with small load are more conducive to comprehensive evaluate the piston crown shape.The research on the matching between the oil beam scheme and the piston shape shows that the oil beam scheme has less influence on the tumble ratio than the piston shape.Compared with the shape of the piston top,the oil beam scheme has a great influence on the fuel wet wall amount of the cylinder liner.Compared with the oil beam scheme,the piston shape has a great influence on the fuel wet wall amount of the piston top.The research on the influence of the injection timing shows that the injection of oil in advance is favorable for the formation of strong tumble flow under2000 r/min@ 0.2 MPa.Under the rated working condition,there is an optimal value at the injection timing(420° CA).too early or too late will increase the fuel wet wall;in the case of the equivalence ratio at ignition timing during the SOI＿380～SOI＿440injection timing,the rated condition will gradually deteriorate with the delay of that,and under the condition of 2000r/min,it gradually became better with the delay of that.The bench test results of the prototype with high flow coefficient intake,smooth gentle slope piston and Spray1 oil beam scheme show that its fuel economy and emission performance are improved compared with the original machine.