Study On Combustion And Emission Of Ethanol/gasoline Combined Injection Engine

Under the current conditions of environmental pollution and energy shortage,energy conservation and emission reduction have become the opportunities and challenges that internal combustion engine industry needs to face currently.As a kind of clean renewable energy,ethanol is simple to prepare,mature in manufacturing process and low in cost.At the same time,its physical and chemical properties have obvious limiting effects on internal combustion engine emissions,and it has become a popular choice for the internal combustion engine industry to find alternative energy sources.In this thesis,on a combined injection engine,ethanol injection(EPI)plus gasoline direct injection(GDI)method was used to explore the ethanol gasoline engine performance under stoichiometric air-fuel ratio and lean combustion conditions.The effect of the ratio of ethanol and gasoline on engine combustion and emissions were emplored.The variables involved in the test included excess air ratio,speed,load,direct injection timing,ignition timing,and alcohol ratio.Through the means of experimentation,the conclusions drawn in this thesis are as follows:Stoichiometric air-fuel ratio:(1)As the proportion of ethanol decreases(G0-G100),the torque gradually decreases and the trend is consistent at either speed.At 180°CA BTDC,the torque decreases with the decrease of the alcohol ratio at each speed.As the speed decreases,the torque increases with each proportion of alcohol.As the load increases,the torque increases with the blending of the alcohol;as the ethanol decreases,the torque decreases for each load.As the proportion of ethanol increases,Tmax shows an upward trend,and the trend is the same at each speed.It can be said that the addition of ethanol improves the combustion condition.At each speed,with the addition of ethanol,the rapid combustion period becomes shorter,indicating that the addition of ethanol accelerates the combustion process and increases the constant volume of combustion.(2)At any alcohol mixing ratio,the cylinder peak pressure gradually becomes larger as the ignition advance angle advances.At the same time,the cylinder peak pressure appears closer to the top dead center and rises rapidly from the cylinder pressure to the upper end.At this point of crankshaft angle,the slope of the cylinder pressure curve is getting larger and larger.At any ignition advance angle,from G0 to G100,as the proportion of gasoline decreases and the proportion of ethanol decreases,it can be found that the crank angle at which the cylinder pressure peak occurs is more and more backward,and the closest to the top dead center are at G0 and G25.(3)As the proportion of alcohol is increased,HC and CO emissions are gradually reduced.As the ignition advance angle is delayed,HC gradually increases,but the effect of ignition advance angle on CO is not obvious;with the advance of direct injection time,CO emission gradually decreasing,HC emissions are gradually rising.As the proportion of alcohol is increased,NOx gradually increases.As the ignition advance angle is delayed,NOx decreases,and NOx decreases as the direct injection timing is delayed.(4)As the proportion of ethanol increases,the number of particles decreases significantly.At the G25 ratio,the number of particles is the least.As engine speed increases,the number of particles decreases,and at 2100 r/min,the particle number is the least.As the load increases,the number of particles gradually increases.At each alcohol blending ratio,there is a spark advance angle with the least number of particles.When the ethanol ratio changes from G25 to G100,the minimum ignition advance angle of the particles is 15°,15°,20°,20 ° CA BTDC,which can be seen.The ignition advance angle at which the number of particles is minimized is advanced as the ratio of ethanol decreases.With the advance of the direct injection time,the number of particles is less and less,and the optimum direct injection time is 180 ° CABTDC.This direct injection time is optimal at any alcohol ratio.In summary,after adding ethanol,the combustion state is improved,and the constant volume of combustion is increased.In the EPI+GDI mode,the proportion of direct injection gasoline is increased,the power is decreased,and the proportion of ethanol in the inlet is higher,and the power is higher.Moreover,in the combined injection mode,the increase in ethanol is very significant for the reduction of emissions,especially for particulates.At the same time,the combined injection mode can easily change the ethanol and gasoline ratio in real time.Lean burn condition:In the case of ? =1.2 and ? =1.4,the MBT(minimum ignition for best torque)point decreases first and then increases with the advance of the direct injection timing.As the excess air ratio increases,the torque of pure ethanol and the maximum temperature in the cylinder are gradually lower than the torque of the gasoline.With the gradual enlargement,NOx decreases first and then increases with the increase of oil blending ratio;HC decreases with the increase of oil blending ratio,while CO is basically unchanged under lean combustion conditions.At any excess air ratio,the amount of particulates tends to increase with the addition of gasoline.