Study On Emissions Of DME/Gasoline Combined Injection Engine

In order to deal with energy crisis,environmental pollution and other issues,as well as more stringent laws and regulations,it is particularly important to find alternative fuels for vehicle fuel,improve engine combustion and reduce emissions.Dimethyl ether is a new kind of secondary energy,known as"clean fuel in the 21st century".It has the advantages of renewable,cheap,fast combustion and pollution-free.Moreover,it is easy to liquefy and store.It is very suitable to be used as an alternative fuel for vehicle fuel.It has high potential and application value for improving the thermal efficiency of engine and reducing emissions.In this paper,the influence of different injection ratio of DME and gasoline inlet on the emission of diesel engine is studied on a compound injection gasoline engine.The main parameters involved in the experiment are DME mixing ratio,ignition timing,injection time,excess air coefficient,speed and load.The content of CO,HC and NO_x in tail gas is the main index of conventional gas emission,while the particle emission index is mainly measured by the number and concentration of particles and particle size distribution.(1)The time of DME direct injection has a great influence on particulate emission.When DME was mixed with mixture,the emission of particulate matter decreased significantly.When the proportion of DME in the mixture increased,the sensitivity of particulate emission concentration to the time of DME direct injection decreased.(2)Whenλ=1,the influence of DME on particulate matter emission is smaller than that ofλ=1.1,1.2 and 1.3.With the increase of excess air coefficient and DME mixing ratio,the particulate emission shows a downward trend.With the increase of DME blending ratio,the number of APN and NPN will decrease under the same condition,and the decrease of APN will be larger.(3)With the delay of ignition timing,the emissions of CO,HC and NO_x are reduced,but the emissions of three kinds of gases are not sensitive to ignition timing.At a fixed ignition timing,with the increase of DME blending ratio,CO,HC and NO_x all showed a downward trend.The particle size distribution of APN and NPN decreased with the increase of DME blending ratio,and the sensitivity of APN and NPN to ignition timing decreased.At a fixed mixing ratio,with the ignition time from 10°CA BTDC to 30°CA BTDC in advance,the nuclear mode particles and accumulated particles show a trend of first slightly decreasing and then rising,with the lowest particle number concentration emission around 15°CA BTDC.(4)At different speeds,CO and HC emissions decreased gradually with the increase of DME mixing ratio,and the higher DME mixing ratio,the more obvious the decrease of CO and HC,the smaller the peak particle number,and the overall trend of APN and NPN.For NO_x emission,at a fixed speed,with the increase of DME blending ratio,NO_x emission will gradually reduce.At a fixed DME mixing ratio,with the increase of rotating speed,NO_x emission shows a trend of decreasing first and then increasing.When the mixture of DME is 5%,the decrease trend of particulate emission is the most obvious.When the mixture is mixed with a small amount of DME,the particulate emission can be significantly reduced.When the mixture ratio of DME is 20%,the amount of particulate emission decreases most than that of PFI.(5)With the increase of load,the emission of CO and HC decreased.For CO emission,when the intake manifold pressure is 40kPa,the decrease range is the largest,when the intake manifold pressure is 50kPa,the decrease range is the smallest,when the intake manifold pressure rises to 60kPa,the CO emission shows a downward trend.For HC emissions,when the intake manifold pressure is 40 kPa and 50 kPa,the mixture of DME can reduce HC emissions,but the mixture of DME has little effect on HC emissions at 60 kPa.For NO_x,with the increase of load,it shows a trend of gradual growth.For each load,NO_x emission shows a trend of gradual decline with the increase of DME blending ratio,and the trend is not obvious.The particle size distribution showed a single peak pattern of increasing first and then decreasing,and the peak range was 10nm-30nm.With the increase of load,the peak value of exhaust particulate concentration increased,and NPN was the main emission.With the increase of DME blending ratio,APN,NPN and TPN decreased gradually.With the increase of load,the effect of DME blending on reducing particulate emission decreased.