An experimental study of stable combustion and flashback phenomenon in a double-layer porous burner

In the current research, a double-layer porous burner has been studied, in which SiC ceramics and alumina silicate (Al2SiO5) balls have been used in the first and second layers, respectively. A very important issue in relation to porous burners is to stabilize the flame on the surface of the porous media. Therefore, it is essential to evaluate the conditions that lead to instability (flashback phenomenon) in order to prevent sudden flashback of the flame in the porous burner. In this paper, the flame temperature, flame stability limit, flashback phenomenon and pollutants formation have been evaluated by changing operating parameters such as diameter of the balls, equivalence ratio and firing rate. Results show that a stable flame prevails in the range of equivalence ratio of 0.35-0.45. The flame moves downstream by reducing the equivalence ratio. Moreover, the maximum flame temperature and the surface temperature decrease by increasing the diameter of the balls. The flame flashback time decreases by increasing the equivalence ratio. In addition, increasing porosity downstream of the burner decreases flashback time. The amount of the excess air has a significant effect on the amount of CO, such that the concentration of CO reduces by reducing the equivalence ratio. The NOx concentration is negligible in all of the experiments (below 5 ppm) due to low temperature of the burner.