Construction And Application Of Dimethyl Ether-biodiesel Blend Fuel Combustion Model

According to the Ministry of Public Security,as of December 2020,the number of automobiles in China had reached 270 million.As the main source of air pollutants,automobile exhaust emissions account for more than 90%of the total vehicle emissions in China.Diesel vehicles account for more than 80%of the total emissions of nitrogen oxides and 90%of particulate matters.Continuously increasing total pollutant emissions and deteriorating environment,resulting in numerous regulations on diesel emissions of carbon monoxide,nitrogen oxides and particulate matters on the increasingly strict control.At present,using alternative fuels to suppress the generation of pollutants at the source of combustion is a mainstream technical scheme to control the pollutants of diesel vehicles.As an alternative fuel,biodiesel has excellent fuel characteristics and can effectively reduce the content of carbon monoxide,unburned hydrocarbons and particulate matters in diesel exhaust.However,considering the high content of unsaturated fatty acids in biodiesel components,it will promote the generation of particulate matters.Therefore,it is an effective way to improve the combustion and emission characteristics of biodiesel by blending with other fuels into biodiesel.As an alternative fuel for fossil fuels,dimethyl ether-plant-derived biodiesel blend fuel can not only make up for the physical and chemical properties of the two alternative fuels,but also improve the emission characteristics of engines.Therefore,in this paper,the combustion and emission characteristics of dimethyl etherbiodiesel blend fuel deserves further investigation,and a dimethyl ether-biodiesel-polycyclic aromatic hydrocarbons skeletal mechanism(DBPSM)model was constructed and applied to the numerical simulation of the working process of the blend fuel engine.The main work contents of this paper are as follows:(1)According to the physical and chemical properties of actual biodiesel,methyl palmitate,methyl stearate,methyl linoleate,methyl-5-decenoate and n-decane with longer carbon chain and higher degree of unsaturated were selected as biodiesel substitutes in this study.Using the decoupling method,a plant-derived biodiesel skeletal mechanism model including 187 species and 982 reactions was constructed.And the optimized skeletal mechanism model was used to validated the ignition delay and in-cylinder combustion of the biodiesel and its components.The validation results show that the plant-derived biodiesel skeletal mechanism model can accurately predict the ignition delay of biodiesel and its components and the combustion condition in the engine cylinder.(2)By combining dimethyl ether(DME)sub-mechanism and polycyclic aromatic hydrocarbon sub-mechanism with plant-derived biodiesel skeletal mechanism,a dimethyl ether-biodiesel-polycyclic aromatic hydrocarbon skeletal mechanism included 255 species and 1253 reactions was constructed.And it is optimized and validated.The results of validation show that the DBPSM model can provide a comprehensive and accurate prediction for the combustion and polycyclic aromatic hydrocarbon emission of DME-biodiesel blend fuel.(3)Based on KIVA3 V2-CANTERA software,the combustion and emissions of four groups of fuels(DME,B5,B10 and B15)in the engine were simulated,and the simulation was compared with the experimental data.The results show that the DBPSM model can well predict the combustion and emission of the blend fuel in the engine.Therefore,this study uses DBPSM to study the combustion and emission rules of the blend fuel in the engine cylinder.The combustion and emissions of four groups of fuels(B100,B90,B80 and B70)in the engine were predicted by DBPSM.The results show that the biodiesel blend with a certain proportion of DME fuel can accelerate the fuel combustion and is more conducive to the cold start of the engine.With the increase of the proportion of DME in the blend fuel,the pressure of the engine also increases,which improves the output power of the engine to some extent.Moreover,with the increase of the proportion of DME,soot and particulate matter have been greatly improved.Therefore,this article constructed the DBPSM model not only can be used to predict many kinds of biodiesel and dimethyl ether and the blend fuel on diesel engine combustion in cylinder pressure,heat release rate,temperature and fuel distribution in cylinder,can also predict biodiesel blending different proportions of dimethyl ether fuel emissions trend.The research carried out in this paper can not only provide a theoretical reference for the study of the combustion and emission laws of ethers-biodiesel blend fuels,but also provide an effective technical path for the realization of energy saving and emission reduction of diesel vehicles.