Combustion Reaction Mechanism Of Diesel Surrogate Fuel And Numerical Simulation Of Pollutant Generation

As an important rail transit equipment for the construction of the “Belt and Road”,the power source is still diesel engine.In order to meet the increasingly stringent diesel emission regulations,there are important theoretical and practiacal significance in the study of pollutant generation characteristics in the combustion process.In this paper,the numerical calculation method of coupled computational fluid dynamics(CFD)of chemical reaction kinetics mechanism is used to study the formation mechanism of soot particles,NOx and unburned hydrocarbons pollutant in direct injection diesel engines.First,considering the similarity of actual diesel component and the physical and chemical properties parameters,a three-component diesel fuel replacement fuel model with 70% n-dodecane,8% cyclohexane and 22% methylnaphthalene(volume ratio)was established.Compared with the existing model,the surrogate fuel model includes three representative hydrocarbon components of paraffin,naphthenic and aromatic hydrocarbons in actual diesel,and fully considers the similarity of the soot threshold coefficient.Therefore,the physical and chemical properties parameters of this surrogate model are more similar to the domestic commercial 0# diesel.Secondly,based on the three-component diesel surrogate fuel model,the chemical reaction mechanism of diesel surrogate fuel combustion was developed,including the formation mechanism of NOx and soot precursor-PAHs.A simplified mechanism includes 98 component and 354 elementary reaction was obtained using reaction flow analysis method.The ignition characteristics and componant characteristics of the model in the zero-dimensional combustion environment were verified by CHEMKIN,which proved the rationality of the combustion chemical reaction mechanism.Moreover,the mechanism of this paper is applicable to the three-dimensional CFD numerical simulation of the diesel engine combustion chamber,and be able to accurately predict the cylinder pressure curve.The 3D CFD calculation model of the diesel engine combustion chamber is established.The simplified mechanism is used,and the detailed soot particle phase model and the moment method algorithm are coupled to realize the numerical simulation of generation of pollutants(soot,nitrogen oxides and unburned hydrocarbons)in the diesel engine combustion chamber.After that,the different injection advance angles 3/7/11/5 BTDC(Before Top Dead Center)and different injection laws(slope,wedge,rectangular and multiple injection)were studied in detail for generation characteristics of pollutant-soot particles,NOx and HC.The study found that the lower the injection time,the lower amount of soot and HC compound pollutants generated,but the amount of NOx pollutants increased;multiple injections can effectively control the amount of pollutant of soot,NOx and HC simultaneously.