Computational and experimental investigation of premixed combustion in porous ceramic infrared heaters

Porous-media radiant burner offers exceptional advantages over traditional free flame burner in that it is a clean, highly efficient heat source with wide regulatory range. Current research on this type of burners lacks quantitative analysis of flame structure and flame stabilization mechanism. In this investigation, a 2D numerical simulation of flame structure inside porous media has been developed. This model is based on a burner element of an industrial thermal-forming machine. Flame position under different combination of air-fuel ratio and fining rate was examined. A series of experiments were carried out on the heat element to gather data of burner surface temperature, pollutant level and overall efficiency. The computational simulation results were compared with these experimental data and showed good agreement for the burner surface temperature. The model developed in this study revealed that there are two different flame modes exist and the flame position moves upon changing the air-fuel ratio and firing rate. Under the assumption employed in the computational model, in the surface stabilized flame mode changing the air-fuel ratio will not change the flame position. On the other hand, in the matrix stabilized mode the flame position will advance downstream as the air-fuel ratio decreases. The transition between these two modes occurs at inlet flow speed of 0.06 m/s ∼0.08 m/s or firing rate of 238.6 Kw/m2 ∼318.2 Kw/m2.; The numerical simulations indicate that the flame speed in the porous media is directly proportional to the firing rate. From energy analysis it was found that surface stabilized flame has much higher radiation efficiency, while in matrix stabilized mode radiation efficiency is lower but can be compensated by higher convective heat transfer due to higher exit gas speed and temperature.