Numerical study of the effect of thermal boundary conditions and porous medium properties on the combustion in a combined porous-free flame burner

The effect of wall thermal conditions, pre-heating of the inlet air-fuel mixture (T-in), and pore density of the porous medium (lambda) on the stability limit and NO emission in a porous-free flame burner is numerically investigated. A reduced chemical mechanism and realizable k-e turbulence model are used for the simulation. The numerical simulation is validated with the experimental data. The results show that the flame stability limit is extended with increasing the pore density while the maximum and minimum NO emissions are produced in pore densities of 8 ppc and 16 ppc, respectively. It is observed that the use of insulated wall condition causes the flame blow-off to occur at higher inlet velocities compared to that of the constant wall temperature condition. On the other hand, the use of constant wall temperature condition (cooled wall), causes flashback to occur in lower inlet velocities compared to that of the insulated wall. Constant wall temperature condition decreases NO emission in comparison with the insulated wall condition approximately by 18%. The flame stabilizes at higher inlet velocities and so stability limit is extended when inlet mixture temperature increases. This also causes NO emission to increase.