Numerical study of flame stability within inert porous media with variable void area

Abstract

This numerical study brings a comparison of a cylindrical porous burner with graded porosity and a conical porous burner with uniform porosity. Both burners have the same void area, creating a similar hydrodynamic stabilization mechanism. The study was performed for a laminar premixed CH4/air flame for different equivalence ratios with the FGM reduction technique employed to model the chemical kinetics. The results demonstrate that the cylinder with graded porosity presents a wider range of stable flames compared with the conical porous burner because the graded porosity leads to a larger heat recirculation as the flame approaches the outlet surface, which is mainly due to an increase of the solid-phase radiative heat transfer. The two-dimensional structure of the flame front was investigated in detail showing that the non-alignment of flow streamlines and solid-phase heat flux lines creates regions of sub-adiabatic and super-adiabatic temperatures along the flame front. Flame area increases with the inlet flow rate with the graded porosity burner presenting a smaller area and larger local consumption velocity than conical burner.