Effect Of DME Blending On Combustion And Emission Characteristics Of GCI Engines

The increasingly severe energy and environmental issues,increasingly stringent pollutant emission standards,and the rapid rise of new energy vehicles in recent years have posed enormous challenges to the traditional internal combustion engine industry.Developing clean and efficient new combustion modes has become an important way to adapt to the current situation.Gasoline compression ignition(GCI)is a "high efficiency,low emission" combustion mode of internal combustion engines,but it has problems of poor combustion stability at low loads and high pressure rise rate at high loads.Dimethyl ether(DME)is an oxygenated fuel with high cetane number,which can be used as an ignition promoter to blend with gasoline to improve the poor ignition performance of gasoline compression ignition at low load.This article adopts numerical simulation method to study the combustion and emission characteristics of gasoline compression ignition under the conditions of dimethyl ether mixing in the small and medium load range(n=1400 r/min,T=330 K),and the effects of dimethyl ether blending ratio and initial boundary conditions on the combustion and emission characteristics of dimethyl ether/gasoline hybrid fuel GCI were analyzed.The main work and research results of this paper are as follows:1)Based on the current mechanisms of dimethyl ether and gasoline surrogate fuel,a mixed fuel chemical reaction mechanism for gasoline/dimethyl ether combustion simulation was constructed and verified;2)Based on the actual shape and size of an engine,the geometric modeling of the engine was built by Solid Works,and the three-dimensional simulation model of coupling fuel chemical reaction mechanism was established by importing CONVERGE numerical simulation software.Based on the literature data,the accuracy of the model was verified;3)Numerical simulations were conducted on the combustion process of GCI engines with different dimethyl ether blending ratios,and the effects of dimethyl ether blending on the combustion and emission characteristics of GCI were analyzed.The results showed that as the mixing ratio of dimethyl ether increased,the peak values of combustion pressure,temperature,and heat release rate in the cylinder gradually increased,the peak phase advanced,the ignition delay period shortened,and the indicated thermal efficiency increased.This indicates that adding dimethyl ether can improve the combustion process of GCI engines;The emissions of carbon smoke,CO,and HC decrease with the increase of dimethyl ether blending ratio,but NOx emissions increase;When the blending ratio of dimethyl ether is 60%,the combustion performance is the best,indicating the highest thermal efficiency,and the emissions are lower at this time.However,when the blending ratio is higher than 60%,the combustion and emission performance of the mixed fuel deteriorates;4)The combustion and emission characteristics of GD60 mixed fuel under different initial boundary conditions were analyzed.The results showed that as the intake temperature increased,the combustion pressure and temperature in the cylinder increased,the combustion phase advanced,but the indicated thermal efficiency decreased;After the intake temperature increases,the emissions of CO and HC decrease,indicating that increasing the intake temperature can improve incomplete combustion in the cylinder and reduce the generation of emissions;As the injection timing is delayed,the combustion parameters such as combustion pressure,temperature,and heat release rate in the cylinder decrease,the ignition delay period prolongs,the center of gravity of the combustion in the cylinder shifts back,the degree of combustion incompleteness increases,and NOx emissions increase;As the load increases,the concentration of fuel mixture increases,the temperature and pressure in the cylinder increase,the ignition delay period becomes shorter,and the combustion center moves forward,which is beneficial for promoting the combustion process in the cylinder.However,when the load is too large,incomplete combustion in the cylinder intensifies,leading to an increase in pollutants such as carbon smoke and NOx.