Research On The Effect Of Fuel Temperature On Combustion And Emission Of GDI Engine

GDI engine has the problem of serious particulate matter emission while improving thermal efficiency.Breaking through this problem is of great significance to the development of in-cylinder direct injection gasoline engine.Increasing fuel temperature has a significant effect on improving the formation and distribution of mixtures in direct injection gasoline engines,which directly affects the formation and secondary oxidation of particulates during combustion of working substances.Therefore,this paper designs an inlet and combustion chamber model for a GDI engine,writes an image processing program,and accurately verifies the model using the constant volume combustion visualization platform and the bench test data.Calculate the effect of fuel temperature on the development of GDI engine spray,the formation and distribution of in-cylinder mixture,the distribution of oil film in the cylinder,the combustion of working fluid and the formation of particulate matter in the single injection mode and the two injection modes,thereby improving the particulate matter emissions problem of GDI engine.The research results are as follows:In the single injection mode,under the condition of 2000 r/min,100% load and equivalent ratio of 1,the effects of fuel temperature and injection parameters on the combustion and particulate matter discharge of the GDI engine were studied.When the injection fuel temperature is raised from 40 ℃ to 100 ℃,the average diameter of the oil droplets is reduced by 5 μm at the same crank angle,which is reduced by 25% compared with the same period of last year;at the ignition timing,the mixture gas equivalent ratio around the spark plug increases from 1 to 1.2,which accelerates the burning speed of the working fluid and increases the maximum burst pressure of the combustion by 2%;the amount of fuel in the cylinder is reduced.when the fuel temperature is 80 ℃ and 100 ℃,the amount of particulate matter in the cylinder at the end of combustion is significantly reduced,reaching the order of 3E-13,which is 105 times lower than the fuel temperature of 40℃.Considering the cost and safety issues caused by fuel heating,80 ℃is selected as the optimal fuel temperature after comparison and analysis.When the injection timing is postponed from 80 °CA to 140 °CA,the distribution pattern of the in-cylinder mixture is more favorable for spark plug ignition and flame propagation,so that the combustion pressure and the peak pressure are increased,and the peak of the heat release rate is increased by 36 J/ Deg,which is 16% higher than that of the previous year.When the injection timing is 140 °CA,the soot mass fraction in the cylinder is in the order of 8.3E-08 at the end of combustion,which is not conducive to the control of particulate matter discharge.Considering the combustion characteristics and emission characteristics,120 °CA is selected as the optimal injection timing.Different injection pressures have little effect on the combustion of working fluids.Under the larger injection pressure,the injection end time is advanced,the distribution of the mixture is more uniform,the combustion pressure is increased,and the peak pressure is advanced.After comprehensive analysis,the optimal injection pressure is selected to be 16 MPa.When the optimum fuel temperature and injection parameters are selected,the combustion thermal efficiency is increased by 1.7% in single injection mode,and the soot mass fraction is maintained in the order of 3E-13 when the exhaust valve is opened.Under two injection modes,the effects of fuel temperature and injection parameters on combustion and soot formation of in-cylinder direct injection gasoline engine were studied.Compared with the single injection mode,the increase of fuel temperature has a greater impact on the mixture formation in the two injection modes.When the fuel temperature is raised from 40 ℃ to 100 ℃,the ignition gas equivalent ratio near the spark plug is reduced from 1.9 to 1.4 at the ignition timing,the mixture equivalent ratio near the injector is reduced from 2.0 to 1.4,and the combustion rate of the working fluid is increased.The maximum burst pressure increased by 3.7% and the peak heat release rate was 215 J/deg.When the fuel temperature is 80 ℃and 100 ℃,the soot mass fraction in the cylinder reaches the order of 1.8E-12 at the end of combustion,which is 103 times lower than the fuel temperature of 40 ℃.After comprehensive comparison,the optimal fuel temperature should be chosen to be 80℃.When the second injection timing is delayed from 120°CA BTDC to 100°CA BTDC,the mixture equivalent ratio of the spark plug increases from 1 to 1.1,the combustion heat release rate increases,and the peak pressure reaches 7.4MPa.After comprehensive analysis,the second injection timing was selected as 100 °CA BTDC.In the two injection modes,the second injection pressure has a greater influence on the combustion characteristics.When the second injection pressure increases from 10 MPa to 16 MPa,the in-cylinder combustion pressure increases,and the peak pressure reaches 7.49 MPa,which increases 7% year-on-year,the moment when the peak pressure appears is moved forward by 2°CA;at the end of combustion,the soot mass fraction in the cylinder is in the order of 4E-13.After comprehensive comparison,the second injection pressure is 16 MPa.Under the two injection modes,the combustion thermal efficiency of working fluid is increased by 2.6% under optimizing fuel temperature and injection parameters,and the soot mass fraction in cylinder reaches the order of 4E-13 at the time of exhaust valve opening,which can better control the particulate matter emission.