Numerical Simulation Of Premixed Combustion Characteristics In A Gradual Expansion Porous Media Burner

Porous media combustion technology belongs to the third generation combustion technology.Compared with similar burners,it has the unique advantages of flexible shape and can be changed according to different application requirements.Therefore,it is necessary to analyze the influence of the different shape and structure of porous media on the internal combustion characteristics and flame stability.It guides the development and application of the burner to find out the best shape and structure of the same type of burner.Compared with the traditional two-layer porous media burner,the expanding porous media burner has stronger radiation performance.Therefore,based on the above advantage,the numerical simulation of premixed combustion of methane/air in a diffused porous media burner is studied.The main research contents are as follows:(1)The influence of flame instability in the expanding porous media burner is studyed.The instability of the flame surface is mainly affected by the internal pressure and velocity,the reason is that there is a pressure difference near the flame surface,the velocity distribution is uneven,and the flow direction is disordered.The magnitude of the inclination angle of the flame surface is affected by the velocity of the combustion wave,and the relative velocity of the combustion wave determines whether the inclination angle of the flame surface increases or decreases.In the range of inlet velocity 0.8～1.2m/s,increasing the equivalence ratio extends the time for the flame surface to reach the maximum inclination angle,and the time for the maximum inclination angle is 1100s.In the range of equivalent ratio of 0.4～0.6,increasing the flow velocity shortens the time for the flame surface to reach the maximum inclination angle,and the time for the maximum inclination angle is 100s.(2)The effects of operating parameters on the temperature change characteristics,combustion self-stability,and pollutant concentration change characteristics are analyzed in detail.In the range of inlet velocity 0.4～0.6m/s,the outlet temperature increases by 139K,the mole fraction of CO increases by 12ppm,and the mole fraction of NOx increases by 8ppm.In the range of equivalent ratio of 0.4～0.6,the peak temperature increases by 433K,the mole fraction of CO increases by 77ppm,the mole fraction of NOx increases by 58ppm,and the inlet velocity range of flame stability is widened.Under the condition of the equivalent ratio φ=0.6,the flashback velocity limit is 0.4m/s,and the blow off velocity limit is 3m/s.In the situation of equivalent ratio φ=0.5 and inlet velocity v=0.5m/s,as the wall heat loss coefficient increases,the wall surface temperature gradually decreases.(3)The effects of gradual expansion angle on temperature change,combustion self-stability,outlet radiation performance,and pollutant concentration change are analyzed in detail.Within the range of gradually expanding angle 0～30°,the peak temperature decreases first and then increases,while the outlet temperature and the wall temperature keep decreasing.The flashback speed limit of the gradually expanding 30-degree porous medium is 0.45m/s,and the blow off speed limit is 3.5m/s,and the inlet velocity range of flame stability is the largest.The radiant thermal efficiency at the outlet of the gradually expanding 10-degree porous media burner is the highest,and its maximum radiant thermal efficiency is 32%.The NOx mole fraction range of the gradually expanding 20-degree porous medium is 20 to 60 ppm,and its NOx emission is the least.