Numerical Simulation Of Supercritical Fuel Injection And Combustion Characteristics

In recent years,with the increasingly serious problem of environmental pollution,emission regulations are becoming more and more strict.Improving combustion performance has become an urgent problem to be solved in the field of internal combustion engine.Some new combustion technologies and new supercharging technologies such as higher injection pressure and higher back pressure have been proposed and widely used in internal combustion engines,which is in order to achieve more efficient and cleaner combustion process of internal combustion engine.With the application of these new combustion methods and supercharging technology,the internal pressure and temperature of the internal combustion engine increase greatly at the injection time.The supercritical fluid has the characteristics of low viscosity,high diffusion coefficient and close to liquid density.For an internal combustion engine,the fuel in a supercritical state injected into the cylinder can effectively improve the turbulent state in the engine cylinder while reducing particulate emissions and achieving clean combustion.In this paper,the jet process of supercritical fuel in constant volume bomb is studied,and the combustion and emission characteristics of the engine are analyzed.In order to explore the mechanism and influencing factors of the supercritical fuel injection process in a constant volume bomb.In this paper,a suitable two-dimensional numerical analysis model is established by using Fluent software,and the flow characteristics of supercritical fuel injection into supercritical environment are numerically simulated.The effects of environmental conditions and fuel states on the supercritical jet characteristics were studied.The results show that the jet length and jet expansion angle are reduced when the ambient pressure increases.The change of ambient temperature has no effect on jet length and jet expansion angle in supercritical jet process.The jet length increases and the injection expansion angle increases slightly as the fuel temperature changes.Supercritical jet length and jet expansion angle increase,with the fuel flow rate increasing,and the increasing trend is obvious.In addition,the similarities and differences between variable density gas injection and supercritical jet are also studied in this paper.The numerical simulation results are in good agreement with the results of the empirical formula by comparing the density distribution and the distribution of fuel mass fraction in the numerical simulation results with the prediction results of the empirical formula of variable density gas injection.Therefore,the empirical formula of variable density gas injection can be used to predict the distribution of fuel in the supercritical jet.In this paper,in order to explore the different of the combustion and emission characteristics between supercritical fuel injection and subcritical fuel injection.AVL-Fire software is used to simulate the operating characteristics of internal combustion engine under supercritical fuel injection and subcritical fuel injection.The changes of temperature,pressure,turbulent kinetic energy,heat release rate,NO emission and soot emission during the operation of the internal combustion engine were studied.The following conclusions are obtained: The ignition time of supercritical fuel injection is slightly ahead of the subcritical fuel injection conditions.The peak value of the cylinder temperature appears a little ahead of time in supercritical fuel injection.The peak value of the cylinder pressure in supercritical fuel injection is large,and the peak value appears at the same time.After a period of time after the fuel is injected into the cylinder,the turbulent kinetic energy increases rapidly in the supercritical fuel injection conditions,resulting in a larger turbulent kinetic energy in the cylinder,which is favorable for the mixing of the fuel and air in the cylinder.Under the supercritical fuel injection conditions,NO emissions increased significantly,and the emission of soot was reduced.