Combustion Simulation Of MDI+GPI Engine

MDI+GPI(Methanol Direct Injection+Gasoline Port Injection)engine uses the antiknock properties of methanol fuel and the advantages of direct injection technology.It can cool the cylinder and enhance the engine resistance by adjusting the methanol injection ratio and methanol injection timing.The purpose of explosiveness and reducing emissions,so that methanol fuel can be used more efficiently in gasoline engines.This paper takes the first cylinder of a naturally aspirated,four-cylinder FPI engine as the basic research object,establishes an MDI+GPI engine combustion model,and analyzes the engine’s working process(flow,spray,and combustion)by injecting different proportions of methanol into the cylinder.),performance and emissions,research on the anti-knock properties of the two fuels(M0 and M20),analyze the engine’s working process(mainly including spray and combustion),performance,and emissions at the injection timing of methanol in the cylinder Impact.The main research includes:(1)Construct a methanol gasoline oxidation kinetic model and laminar flame data table for the 3D combustion model(G equation and SAGE model)to call,and analyze the laminar flame velocity and spontaneous ignition delay period under different MDI ratios.The results show that the mixing of methanol in gasoline can increase the laminar flame velocity of the fuel and increase the spontaneous ignition delay period in the low-temperature combustion stage.The larger the mixing ratio,the more obvious the effect.(2)Use the constructed methanol gasoline oxidation mechanism and laminar flame data table to establish a three-dimensional combustion model and verify the accuracy of the model,and study the effects of different MDI ratios on the engine’s working process(flow,spray,and combustion),performance and emissions.The results show that when the MDI injection mode is adopted,the average turbulent kinetic energy in the cylinder can be enhanced during the spray phase,and at the same time,the turbulent kinetic energy distribution in the cylinder at the moment of ignition can be improved;in general,the methanol in the cylinder evaporates faster in the intake phase than in the compression phase.,M60,which accounts for the largest volume of methanol,can also evaporate 92% before ignition.When the proportion of MDI is small,such as M20,it can completely evaporate and form a more homogeneous mixture than M0 at the moment of ignition.When the proportion of MDI is high,such as M40 and M60,the methanol fuel that is not completely evaporated will form more Coanda oil film before ignition;the flame propagation speed of M20 and M40 will be faster than that of pure gasoline fuel(M0),which has a shorter The ignition delay period and combustion duration period,the cylinder can have a greater indicated average pressure.The flame propagation speed of M60 is equivalent to that of M0,which may be affected by the decrease in the temperature in the cylinder and the decrease in the quality of the methanol fuel evaporation mixture,and the ignition delay period of the fuel becomes longer.The engine performance obtained by burning methanol fuel is better than M0;the SOOT emission of M0 is higher than other simulation cases,the NOX emission of M20 and M40 is the highest,and the CO and HC emission of M20 is the least.(2)Take M0 and M20 as examples to compare their combustion characteristics and anti-knock properties at different compression ratios.The results show that as the compression ratio increases,the temperature in the cylinder at the moment of ignition increases,the working fluid density in the cylinder increases,the flame propagation speed increases,the spontaneous ignition delay period and the combustion duration become shorter,and the indicated average pressure increases;for M0,when A slight knock occurred when the compression ratio was 12.0,and when the compression ratio increased again,the knock index rose sharply.For M20,as the compression ratio increases,the knock index changes less than M0.When the compression ratio is 13.0 and there is a slight knock,the knock index only slightly fluctuates upwards.(3)Analyze the evaporation process of methanol and the mixing situation at the moment of ignition under different MDI moments.The results show that the methanol evaporation speed is relatively fast when the intake valve opening is large and in the later stage of the compression stroke.The later the MDI time,the lower the methanol evaporation rate,the more uneven the distribution of the mixture and the unevaporated fuel,but it may cause greater turbulent kinetic energy in the cylinder at the moment of ignition.When the MDI time is earlier or later,such as MDI-250 and MDI-100,the flame propagation speed is faster and the ignition delay period is shorter.At the same time,the explosion pressure in the cylinder and the indicated average pressure are also larger.The homogeneous mixture,the latter is mainly due to the strong turbulent kinetic energy near the spark plug;when the MDI injection time is late,such as MDI-100,more Coanda oil film quality causes higher CO emissions.