Investigation On Flame Characteristics Of Varied Axial Cross Section Porous Medium Burner

Porous media combustion technology has a series of advantages,such as high combustion rate and combustion intensity,low pollutant emission,large heat load regulation ratio,wide lean combustion limit,small volume and flexible shape,etc.,and the study of combustion characteristics in porous media has become one of the hot spots in the field of combustion in recent years.Due to the flexible shape of the porous media burner and the advantage that the shape can be changed according to different application requirements,the influence of the structure of the porous media on the internal combustion characteristics and combustion stability of the porous media is explored,which plays a guiding role in the development and application of the burner.Based on Fluent16.0 simulation software,the combustion characteristics of methane in a porous medium burner were simulated.Uses the porosity of foam ceramics is modeled and fluid-structure coupling heat transfer boundary conditions,explore gas in divergent type,and the combustion characteristic of reducing type within porous medium burner and combustion stability,reveals the change of inlet air flow direction on the flame,hot spot of the incline and the influence law of drawing,splitting,the results showed that:(1)the axial flow rate and pressure drop value of gas in the burner with gradual expansion structure under cold condition are far less than those in the cylindrical structure with the same base and height.Gradually expanding porous media structure reduces gas flow rate and makes combustion more stable.It is less affected by the initial pressure,which is helpful to prevent tempering and to widen the lean combustion limit of the gradually expanding porous medium burner.In the comparative analysis of five progressive expansion angles,Porous media burner with a progressive expansion Angle of 10 has the widest combustion limit range.The velocity of flame surface movement and the maximum temperature of combustion zone are greatly affected by the equivalent ratio,inlet velocity,gradual expansion Angle and other factors.With the increase of the equivalent ratio,the maximum temperature in the combustion zone increases and the flame propagation speed decreases.As the inlet velocity increases,the maximum temperature in the combustion zone decreases and the flame propagation velocity increases.Increasing the Angle of gradual expansion will reduce the flame propagation speed,but has no effect on the maximum temperature in the combustion zone.(2)the axial flow rate and pressure drop value of gas in the burner with tapering structure under cold condition are much higher than those in the cylindrical structure with the same base and height.The velocity of gas in the tapered structure is accelerated,so the combustion speed is increased.However,due to the influence of the shrinking structure,the pressure drop of the air flow is large,the flow velocity in the burner is fast,and the combustion limit range is low.The combustion limit of the structure with 10 degrees of shrinkage was the highest and slightly higher than that of the cylindrical structure.As the decreasing Angle increases,the combustion limit decreases.The velocity of flame surface movement and the maximum temperature of combustion zone are greatly affected by the equivalent ratio,inlet velocity,taper Angle and other factors.The maximum temperature and flame propagation velocity in the combustion zone increase with the increasing of the decreasing Angle.(3)the combustion stability of methane/air in a burner with variable inlet flow direction was simulated and analyzed.The simulation results reveal the law of unstable phenomena such as flame surface tilt,stretching,hot spot generation and separation.Hot spots appear when the flame surface is tilted at an Angle of 61,the number of hot spots as the inlet velocity increases with increasing.The separation of flame surface is related to the inlet velocity and the inlet airflow direction.When the gas reaches the porous media region of the tapered inlet structure,the flow rate is greater than that of the tapered inlet structure.The higher the equivalent ratio,the lower the flame combustion position,and the combustion starts from local combustion.