Research On Multi-component Surrogate Fuel Of Diesel Based On Physical And Chemical Properties

This paper starts with the physical and chemical properties of diesel fuel and summarizes the difficulties faced in the construction of current diesel surrogate fuels.(1)Common diesel characterization models can not reproduce the physical and chemical properties of diesel well,and there are certain deviations in the prediction of diesel combustion and emissions.(2)As far as the construction method of diesel surrogate fuel is concerned,there are shortcomings of insufficient versatility.Regarding the issue above,based on the Decoupling Physical-Chemical Surrogate(DPCS)model,this paper established an optimizer that characterized the physical and chemical properties of real fuel to effectively formulate diesel surrogates.Ten physical candidates(n-decane,n-hexadecane,n-eicosane,2,2,4-trimethylpentane,2,2,4,4,6,8,8-heptamethylnonane,ethylbenzene,tetrahydronaphthalene,1-methylnaphthalene,methylcyclohexane,and cis-decalin)and four chemical candidates(n-decane,2,2,4-Trimethylpentane,methylcyclohexane,and toluene)were employed to construct the DPCS model.The physical and chemical candidate components were selected from four typical hydrocarbons in real diesel and were coupled according to the hydrocarbon type.In the optimization part,the composition ratio of physical components was selected as the optimization parameter.The objective function was established by evaluating the error of the physical and chemical properties between the surrogate fuel and the real diesel,and the genetic algorithm was used to optimize.To verify the reliability of the optimizer,surrogate fuels of different types of diesel were optimized and constructed.The optimization results show that the surrogate fuels constructed in this paper reproduce the physical and chemical properties of different types of diesel.In addition,the results of surrogate fuel predictions were compared with experimental data,including the spray and ignition characteristics of constant volume bomb and the combustion and emission characteristics of conventional diesel combustion(CDC)engine.Numerical simulation results show that the surrogate fuels formulated by the current method reproduce the spray,ignition,and emission characteristics of different diesel fuels.In terms of the validation of the constant volume bomb(CVB),diesel with lower distillation curves(F3 and F4)predicts more vapor fuel on the spray axis,and the content of n-decane in the vapor components of diesel F1,F2,and F4 decreases successively,the reactivity of the vapor fuel downstream of the spray decreases,and the ignition delay time increases sequentially.As far as engine validation is concerned,compared with common surrogate models,the combustion and emission results predicted by the DPCS model are more consistent with the experimental data,especially for the prediction of low cetane number diesel.In addition,the DPCS model was employed to study the combustion and emission characteristics of diesel with different physical and chemical properties.The results show that the surrogate fuels constructed by this method can well reproduce the influence of the difference in fuel distillation characteristics on fuel evaporation.Besides,through the chemical kinetic analysis of the computational grid,it is found that the high reactivity component(n-decane)in the chemical surrogate fuel dominates the ignition characteristics of the fuel,and the ignition time further affects the emission characteristics of the fuel.As far as the CDC engine is concerned,the physical characteristics of the surrogate fuel will affect the formation and distribution of the vapor fuel,thereby indirectly affecting the ignition characteristics.The chemical properties of the surrogate fuel are the main factors governing combustion and emissions,especially the cetane number and aromatic content of the fuel.With the increase of aromatics content in diesel,the reactivity of fuel delines,the delay of ignition time and fuel-air premixing degree before ignition increase.The combustion heat release rate,in-cylinder temperature and pressure,and NOx emission increase.Besides,due to the increase in aromatics content,the wall quenching effect and incomplete combustion are intensified,thereby increasing HC emissions.