Numerical Simulation Study On The Combustion Characteristics Of High Pressure Methane Jet Impingement Premixed Flame Inside A Constant Volume Bomb

Natural gas internal combustion engines with direct in-cylinder injection technology have better thermal efficiency and emission performance than inlet tract injection technology.The essence of the combustion process is diffusion combustion,where the natural gas injected interacts with the initial premixed flame to form a violent non-homogeneous turbulent combustion.In this thesis,using the direct-injection natural gas internal combustion engine as the research background,combined with the experimental data of high-pressure methane jet impact premixed flame in the constant volume bomb,and using CONVERGE software to carry out multi-conditions simulations on multiple variables of dilute and rich combustion equivalence ratio,ignition and jet time interval t_d,the distance between ignition position and nozzle outlet D_i and studied the action law of the above parameters on combustion characteristics,the following main conclusions were obtained.(1)Under rich combustion conditions,the addition of methane high-pressure jet makes part of the premixed flame become turbulent combustion flame,and the flame will go through three stages of stabilization-destabilization-attaining a new steady-state process.In the first stage,the flame is a stable premixed flame;in the second stage,the initial premixed flame induced by the jet becomes unstable,and the combustion and turbulence parameters change dramatically,t_d is inversely proportional to the maximum value of the flame surface area change rate and proportional to the maximum of the turbulent kinetic energy change rate;in the third stage,a steady-state of turbulent combustion flame and premixed flame coexist,and the flame propagation speed tends to be stable.(2)Under dilute combustion conditions,the high-pressure methane jet contacts the premixed flame,and then the jet front forms a diffusion flame surface and the initial premixed flame surface coexist and develop,and the dominant combustion mode in the fixed capacity bomb changes from the premixed flame surface to the diffusion flame surface.With the increase of distance D_i between ignition position and nozzle exit,the initial flame structure develops from jet peripheral ignition to jet front ignition.The initial combustion performance of the working jet injection with jet front ignition is good,the later combustion performance of the working jet injection with jet peripheral ignition is morerior,and the optimal ignition position is found to exist.(3)The variation of t_d and D_i with jet injection time on the effect of combustion and turbulence parameters was analyzed for dilute and rich combustion conditions.For?=1.0,the positive correlation between the rate of increase of turbulent kinetic energy and t_d was significant with the increase of jet injection time,and the effect of t_d on the rate of increase of combustion exotherm was gradually weakened;for?<1.0,the effect of t_d and D_i on combustion exotherm was more significant at the beginning of jet injection,and the effect of both parameters on turbulent kinetic energy was more intense at the end of jet injection.In the later stage of jet injection,the effects of the two parameters on turbulent kinetic energy are more dramatic,and the smaller the equivalent ratio,the less sensitive the combustion exotherm and turbulent kinetic energy are to t_d.