Experimental investigation on flame characteristics in a porous-free flame burner

Present work studies experimentally the flame characteristics of a premixed natural gas/air mixture in a porous-free flame (PFF) burner, and also it is compared with a conventional porous burner. For the PFF burner a hole is created at the center of the porous foam, which has a porosity of 87%, height of 22 mm and diameter of 90 mm, making a combination of a free flame and a flame in the porous region. Effects of the hole diameter, d = [6, 9 and 12 mm], foams pore density, λ = 10, 20 and 30 pores per inch (ppi), and foam materials (SiC and Al2O3) on the axial temperature distributions of the foams as well as on the lean and rich limits are examined. The results show that for a fixed foam pore density and foam material, the axial temperature of the foam in the PFF burner is lower than that of the porous burner. Also, for the PFF burner an increase in the hole diameter leads to a decrease in the axial temperature. Compared to the PFF burner, the flame in the porous burner is stabilized at a lower equivalence ratio (leaner mixture), while the PFF burner extends the rich limit of the flame. Additionally, the diameter of the hole found to have insignificant influence on the lean and rich limits. Results further show that an increase in the foam’s pore density leads to a decrease in the axial temperature of the foam and the lean/rich limit of the flame. The axial temperature of the SiC foam found to be higher than that of the Al2O3 porous foam. Furthermore, the lean and rich limits are extended by deploying the SiC porous foam.