Numerical Simulation On Premixed Combustion Of Methane-air Under Variable Turbulence

The problems of energy shortage and environmental pollution have become increasingly serious.How to effectively and reasonably organize the combustion process of the engine has become an urgent problem to be solved.Gas fuel has great potential and broad application prospects in solving the shortage of petroleum resources and environmental degradation,and turbulent premixed combustion is an effective combustion method in the actual working process of gas fuel engines.The premixed combustion process of gas fuel has been simulated and calculated,which has certain theoretical significance and engineering application value for improving engine power and economy,and reducing pollutant emissions.This paper is based on a new turbulent constant volume combustion bomb experimental system for numerical simulation of gas fuel turbulent premixed combustion.According to the basic governing equations of fluid mechanics,the gas flow and combustion process in the system were theoretically analyzed.The time-averaged method was used in the mixture formation process,and the large eddy simulation method was used in the combustion process to establish a turbulent flow model of gas fuel for a constant volume combustion bomb.The Premixed Combustion combustion model was used to complete the establishment of a mathematical model of premixed gas fuel burning in a constant volume combustion bomb under turbulent flow.Based on the above model,FLUENT was selected as the simulation platform.The sensitivity analysis of grid size and time step were carried out.Meanwhile,the calculation results were compared with the experimental data to verify the accuracy of the simulation model.The turbulent flow process of methane-air mixture in the constant volume combustion bomb was studied.It was concluded that as the motor speed in the turbulence generating system increased,the overall turbulence intensity at the center of the constant volume combustion bomb increased.The methane-air premixed turbulent combustion process was simulated,the front structure of the turbulent flame was further analyzed,and the effect of the vortex on the flame surface during the turbulent flow was described.The analysis of the methane-air premixed combustion characteristics under variable turbulence found that the introduction of turbulence can significantly accelerate the flame propagation speed,flame elongation,flame front wrinkle degree,combustion velocity,and the increase of pressure and temperature.The corresponding peak pressure and temperature increased.An analysis of the influencing factors of methane-air premixed combustion in a turbulent environment was carried out.The results show that higher initial temperature and initial pressure accelerate the flame propagation and promote the combustion process.The increased ignition energy in the early stage of combustion will accelerate the flame propagation.But as the combustion progresses,the effect of the ignition energy is smaller.The flame propagation under the stoichiometric conditions is the fastest,and the combustion is the most violent.Rich combustion is more conducive to flame propagation than lean combustion.Increasing the initial temperature will shorten the time to reach the peak and the increase rate of the combustion temperature.The corresponding peak value will decrease.Higher pressure will obtain the maximum combustion pressure and pressure increases more slowly.But the corresponding value and the combustion heat release rate increases.The increase in ignition energy will accelerate the rate of increase in combustion pressure and temperature,shorten the combustion time so that the peak can be reached faster and the peak increases.