Numerical Simulation For High Pressure Injection And Combustion Characteristics Of Gas Fuel

For direct-injection gaseous engines,the injection characteristics and combustion characteristics of the fuel are the keys to the engine’s power and emissions characteristics.Therefore,it is necessary to study the injection and combustion process of gas fuel.Because of the characteristics of the high pressure gas injection and the interaction with the turbulence in the cylinder,the mixing and combustion process of the direct injection gas fuel is complicated and changeable.In this paper,Mixing and turbulent combustion process of gas fuel is taken as the research object.Fluent is used as simulation platform to simulate the characteristics of high pressure injection and combustion characteristics.The effects of different factors on injection characteristics and combustion characteristics of gas fuel are studied.In this paper the basic control equation of fluid mechanics and the theoretical analysis of the turbulence model are carried out.Based on the structure and working mode of the turbulent constant volume combustion chamber system,a simulation model of high pressure injection for gas fuel is built on the basis of Realizable k-ε turbulence model.It can be used to simulate and calculate the high-pressure injection process of gas fuel under turbulent conditions,and to carry out the coupling analysis of the turbulent flow field of the high pressure injection and the isotropic turbulence field generated by the turbulence generator.The simulation results of the simulation model and the experimental data are compared and verified.Based on the model above,the simulation model of high pressure injection combustion of gas fuel is established on the basis of the vortex dissipative combustion model.A single step total package is used to simulate the chemical reaction mechanism in the combustion process of gas fuel,and the accuracy of the numerical simulation model was verified.The high pressure injection simulation model of gas fuel is used to simulate and analyze the high pressure injection of gas fuel.The distribution of the concentration field,velocity field,temperature field and turbulent kinetic energy of the high pressure injection of gas fuel at different injection times is calculated.The effects of different injection pressure,nozzle diameter,back pressure and initial turbulence on gas fuel high-pressure injection penetration distance,near field cone angle,injection front velocity and concentration distribution were analyzed.The results show that,compared with the environment without initial turbulent flow,the initial turbulent flow field in constant volume combustion chamber accelerates the radial development of gaseous fuel injection.However,it is beneficial to the axial diffusion of gas fuel,and leads to the decrease of the penetration distance of the gas fuel injection and the increase of the conical angle of the near field.The simulation of high pressure injection combustion of gas fuel is studied by using the combustion model.The distribution of the reactant,the concentration and the temperature distribution in the combustion process of the gas fuel injection are calculated.The combustion gas structure,flame velocity distribution and flame temperature distribution of gaseous fuel injection under different initial pressure,spray hole diameter,back pressure and initial turbulence were compared and analyzed.The effects of different factors on the combustion characteristics of gas fuel injection are studied.The results show that the initial turbulent flow field accelerates the velocity of flame propagation in the space,and promotes the development of the length and width of the flame.