Study On The Combustion Characteristics Of Dimethyl Ether Blends

With the development of the economy,the imbalance between the energy supply and demand is becoming more and more serious,and the problem of environmental protection is worsening sharply.Researches and developments in new energy vehicles have been paid more and more attention.Dimethyl ether(DME)is a new renewable clean alternative fuel with high efficiency and low emission and receives the greatest attention.A large number of engine tests show that DME blends can achieve better combustion performance,higher fuel economy and lower engine emissions.However,the fundamental research on combustion of DME blends is deficiency,and the combustion details of DME blends are unclear.In this study,the effects of hydrogen,methane,ethane and propane on the laminar combustion characteristics of dimethyl ether are systematically studied.The emphasis is on analyzing the effects of fuel addition on the laminar combustion speed and flame stability.The main conclusions are as follows:The study on the laminar combustion characteristics of fuel blends under different equivalence ratio,initial pressure and mixing ratio shows that the laminar flame speed increases firstly and then decreases with the increase of equivalence ratio,and the maximum value of that is obtained at the slightly richer mixture.This is because in the lean or the rich mixtures,the fuel or the oxidant is inadequate,which would result in the reduction in the reaction rate.With the increase of initial pressure,the increase in density of the unburned mixture would account for the decrease in the laminar flame speed.The results show that stability in the flame surface is mainly affected by the preferential diffusion under the different equivalence ratio.Combustion of the fuel blends show characteristics similar to dimethyl ether under the low blending ratio,and the richer mixtures have the better flame stability,while,at the high blending ratios,the combustion of the fuel blends show characteristics similar to the mixed fuel.With different kinds of fuel addition,the different molecular structure and molecular mass are the main reasons for the difference of laminar combustion characteristics.Hydrogen addition increases the flame speed,while alkanes addition decreases it.This is mainly due to the change in the concentration of important free radicals in the reaction by different fuel addition;The study on Markstein length in different fuels addition show that the flames wouldbe more stable with ethane and propane addition,while it would be more unstable with hydrogen and methane addition.This is mainly because the deference in the preferential diffusion and thermal diffusion of the mixture caused by different kinds of fuel addition.