Effects Of Combustion Zone Structure On Premixed Combustion Characteristics In Porous Media

Porous Medium Combustion is a new combustion technology with high combustion efficiency,large heat load regulation ratio and low pollutant emission,and has broad application prospects.In this paper,the optimization and improvement of the two-section porous medium burner are carried out.The influence of the combustion zone structure on the premixed combustion characteristics in the porous medium is studied.The main research includes:1.Study the influences of the thickness of the combustion zone on the premixed combustion characteristics in the porous medium to find the optimal thickness ratio of the combustion zone and the preheating zone,and broaden the stable combustion range of the burner.2.The effects of aperture distribution along the radial direction in the combustion zone on the premixed combustion characteristics in the porous medium is studied to improve the phenomenon of inclination flame in the porous medium,making the burner more efficient and less polluting.In this paper,a two-section ceramic porous medium burner experimental platform consisting of silicon carbide is built initially.Methane and air are burned in the porous medium burner with different thickness and aperture distribution along the radial direction in the combustion zone.The combustion characteristics such as temperature and pollutant emissions are measured.Then,based on the experimental research,a two-dimensional transient two-temperature mathematical physics model of the two-section porous media burner was established by using FLUENT16.0 software.The effect of combustion zone thickness and the radial pore diameter variation in the combustion zone on the combustion characteristics such as stable combustion range,pollutant emissions,and radiant heat efficiency in porous media are numerically simulated.Compared with experiments results,the following conclusions were obtained:(1)With the increases of the thickness of combustion zone,the overall average temperature in the burner decreases,and the outlet mass fractions of NOx and CO gradually decrease.With the increases of the thickness ratio,the combustion stability interval firstly increases and then decreases.When the thickness ratio of the combustion zone to the thickness of the preheating zone is 3,the stable combustion interval is the largest.The thinner the thickness of the combustion zone is,the higher the outlet radiant heat efficiency is,but the stable combustion zone is very narrow.Considering comprehensively,under the same combustion conditions,when the thickness ratio is three,that is,the thickness of the combustion zone is three times the thickness of the preheating zone,the burner has the best combustion effect.At this time,the stable combustion interval is the largest,and the combustion radiant heat efficiency is also relatively high.(2)The porous medium model with radial aperture variation in the combustion zone effectively solves the problem of the inclination flame,broadening the stable combustion interval,improving the overall temperature level of the burner,and making the temperature distribution in the burner more uniform.Under the same working conditions,the internal encrypted porous medium model has the most uniform outlet temperature.In practical production applications,an internal encrypted porous medium model is the best choice for processes that require uniform heating of objects.Two types of encrypted porous medium model with radial aperture variation in the combustion zone can improve the radiant heat efficiency of the burner,when the equivalent ratio is 1.0,the radiant heat efficiency of the internal encrypted porous medium model and the external encrypted porous medium model is improved by 14%and 10%respectively,compared with the unencrypted porous medium model.Two types of encrypted porous medium model with radial aperture variation in the combustion zone can reduce CO emissions,when the equivalent ratio is 1.0,the internal encrypted porous media model can reduce CO emissions by nearly 12%,the external encrypted porous media model can reduce CO emissions by approximately 7%.