Investegation On Chemical Kinetic Model And Multi-dimensional Numerical Simulation Of Gasoline Surrogate Mixtures For Supercritical Combustion

Gasoline direct injection engine(GDI)can accurately control the injection timing and fuel injection quantity and improve the fuel economy of gasoline engine,has gradually replaced the port fuel injection(PFI)technology become the mainstream technology of gasoline engine.However,the particulate matter(PM)emissions of the GDI engine are greater in quantity and quality than the PFI gasoline engine.In order to effectively reduce the emission of particulate matter,supercritical combustion technology has been proposed.Supercritical fluid has the advantages of low viscosity and high diffusion coefficient.The supercritical combustion of gasoline can effectively reduce particulate matter,which is one of the effective ways to achieve efficient and clean combustion.In this paper,the chemical kinetic model of gasoline under supercritical conditions is proposed.Then the mechanism is coupled with the calculation model in CONVERGE software,and the supercritical combustion of gasoline is compared with subcritical combustion by adjusting the injection strategy.The difference can provide guidance for the research of supercritical combustion technology.This study proposes a modifying mechanism for simulating supercritical gasoline;this mechanism contains 103 species and 201 reactions and is obtained by modifying the pre-exponential factors of key reactions and adding key reactions on the basis of the original mechanism proposed by our research program.The modifying mechanism is validated by a comparison with the experimental data of Fuel C,Surrogate A,Surrogate B,and each single component(iso-octane,n-heptane,and toluene).The simulation results agree with the experimental results,and the modifying mechanism can predict the various tendencies of ignition delay time with pressure and temperature.Then the three-dimensional calculation model is built based on the geometric model of a GDI engine.The grid size of calculation is 4mm,2mm and 1mm,and the adaptive mesh refinement(AMR)technology is adopted based on the velocity gradient and the temperature gradient.Grid independent verification for numerical simulation based on the three-dimensional model of a GDI engine is conducted from the mean in-cylinder pressure and mean in-cylinder temperature,and the grid size of subsequent calculations is set to be 2mm.Validity of the model is verified by experimental data of in-cylinder pressure.Supercritical gasoline combustion characteristics are studied by coupling the three-dimensional calculation model with the chemical kinetics model proposed by this paper.In order to further to explain the difference between supercritical and subcritical combustion,the subcritical combustion process is simulated by changing the injection strategy.The results show that the air-fuel mixture of supercritical gasoline is better than subcritical gasoline and burned fully,so that the peak temperature and peak pressure in supercritical combustion are higher than that of subcritical combustion.The supercritical combustion can significantly reduce soot and CO emissions.Compared with subcritical combustion,the soot emissions of supercritical combustion reduced87%,and the CO emissions reduced 86%,but the NO_x emissions increased.Finally,in order to investigate the effect on the supercritical combustion of different conditions,the research on different intake pressure and different intake temperature are conducted.The results show that with the increase in the intake pressure,the mean pressure and mean temperature decrease,and the soot emission decrease,and the NOx and CO emission increases first and then decreases.When the intake temperature increases,the mean temperature increases,and there are no obvious change in the peak pressure,the emission of soot and CO decreases,but the emission of NOx increases.