Flame Structure And Combustion Characteristics Of Premixed CH4/Air Jet Flame Under The Effect Of Wall

Most practical combustion systems have wall surfaces,which strongly affect the combustion process in terms of gas dynamics,thermodynamics,and reaction kinetics.In fact,flame and wall interaction is one of the main mechanisms for the emission of unburned hydrocarbon chemicals.As the emission requirements become stricter,the requirements for the efficiency of the combustion system and the limits of hydrocarbon emissions.It is urgent to study the two-way coupling process of flame and wall interaction.This can not only provide a theoretical basis for the design of engines and various types of combustion chambers,but also enrich the theory of near-wall combustion inside the combustion device in practical applications.Based on the research status of flame-wall interaction between domestic and foreign scholars,the flame structure and combustion characteristics of premixed methane/air jet flame under the effect of wall were experimentally and numerically investigated.The research contents and results with significance have been acquired as follows?1?A visualized experimental test platform was built to study the flame and wall interaction.A two-dimensional numerical model of premixed methane/air combustion under the effect of wall was established,which based on the relevant parameters of the experimental bench and the mechanism of the chemical reaction.At the same time,the simulation results are in good agreement with the experimental results.?2?Compared with the jet flame without the effect of wall,the influence of different Reynolds numbers on the flame characteristics of the CH₄/Air premixed under the effect of wall was investigated by the combination of experiment and numerical simulation.The results show that the length of the premixed cone profile under the effect of the wall is shorter than the condition without wall.The presence of the wall can inhibit the flame from stretching downstream,reducing the height of the premixed cone and increasing the width at the tip of the premixed cone.The temperature gradient and velocity gradient increased near the wall surface.The presence of the wall changed the speed in the axial direction and increased the maximum pressure value near the tip of the premixed cone and the overall pressurelevel.?3?The influence of the wall position on the premixed combustion characteristics of CH₄/air was obtained by numerical simulation and experimental study.The results show that with the increase of the burner-to-wall separation distance?ie.separation distance?,the premixed cone changed from a trumpet shape to a complete cone,and the length of the premixed cone profile gradually increased.When the lowerwall surface was above the tip of the premixed cone,with the separation distance increased,the height of the premix cone gradually increased,but the increase rate gradually decreased;the peak value of temperature and velocity on the central axis increased,and the peak value and corresponding axial distance of net reaction rate of reactant?CH₄?,intermediate product?CO?and product?CO₂,H₂O?on the central axis also increased.In addition,when the lowerwall surface was closest to the tip of the premixed cone,the temperature peak and velocity gradient of the gas near the wall were the largest.The intensity of chemical reaction near the wall increased with the decrease of separation distance.With the increase of separation distance,the emission factor of CO?EICO?first increases,then decreases and tends to be stable finally.?4?The effect of wall physical properties on the combustion characteristics of the CH₄/Air jet flame near the wall was studied by numerical simulation.The results show that as the thermal conductivity of the wall decreased,the gas temperature near the wall increased and the temperature gradient decreased.And the increase of the wall thermal conductivity can enhance the reaction strength between CO and OH,resulting in the increase of CO₂ concentration.The heat transfer strength at the gas-solid interface increased with the increase of the wall thermal conductivity.As the heat dissipation of the wall increased,the temperature of the wall gradually decreased,the temperature of the gas near the wall decreased,the intensity of the chemical reaction near the wall weakened,and the intensity of heat transfer at the gas-solid interface increased.