Numerical And Experimental Study On The Combustion Process Of Diesel/Ethanol Dual-fuel Engine

With the rapid development of the automotive industry,the number of domestic car ownership has also increased year by year.The increase in the number of vehicles which are driven by energy consumption means that the increase in energy consumption and the emission of harmful substances of the vehicle will bring more pollution to the environment.In the face of the two major problems of energy consumption and environmental pollution,the development of renewable clean alternative energy sources is very meaningful to reduce dependence on traditional energy sources and improve living environment.Ethanol is one of the renewable and clean alternative fuels,and a large number of experiments and numerical studies on the blend of ethanol in diesel engine show that ethanol has a great potential in diesel engines.Based on the above background and significance,the method of CFD numerical simulation and bench test are used to explore the effect of mixed fuel with different ethanol blending ratio on the combustion and discharge of diesel engine.Firstly,the mechanism of Diesel/ethanol mixed fuel containing PAHs generation was constructed by means of path analysis and sensitivity analysis through CHEMKIN package.The ignition delay in shock tube,the concentration of important component in laminar flame and multi-dimensional numerical simulation in AVL-FIRE software of the mechanism were verified,and the results showed that the mechanism can better describe the combustion of diesel/ethanol mixed fuel and the generation of the combustion product.Secondly,the model of the engine is constructed by the 3D CFD software AVL-Fire,and the simulation of the combustion and emission of the mixed fuel with different ethanol blending ratio was carried out by the coupling of the validated mechanism.Simulation results showed that,the addition of ethanol increases the ignition delay of the mixed fuel,and increases the concentration of O and OH in the engine,which will accelerate the combustion in the cylinder,and the temperature will increase.At the same time,the oxidation of CO,C₂H₂,PAHs and soot is enhanced,and the formation of NO is reduced.However,the increase of temperature and the increase of O are beneficial to the formation of NO,which leads to the increase of NO.Finally,the diesel engine bench test was carried out in this thesis.By changing the proportion of ethanol in diesel oil,the cylinder pressure,exhaust emissions and fuel consumption data was measured under different load,fuel injection time and EGR opening condition of diesel engine.The influence of ethanol addition was studied in many aspects.Especially,the mass,quantity and size distribution of diesel particulate emissions were studied by DMS500 particle analyzer.The experimental results showed that ethanol has a similar effect on diesel engine under different operating conditions.At low load,the addition of ethanol makes the diesel cylinder pressure drop,and in the high load,the addition of ethanol makes the diesel engine cylinder pressure increased significantly.The ignition delay time becomes longer and combustion duration becomes shorter with ethanol addition.At the same time,brake thermal efficiency is improved with the increase of ethanol fraction.With the increase of ethanol addition,the number concentration of all soot particles shows an upward tendency,on the contrary,the mass concentration of soot particles is decreased.Meanwhile,the peak of particle size distribution function?PSDF?moves forward.In addition,NOx emission will increase with the increase of ethanol fraction.Through the combination of theoretical calculation and experimental research,the influence of ethanol on the combustion and emission of diesel engine has been discussed more deeply,which will provide some reference for the application of ethanol on diesel engine.