**2.1. Stability of flame**

The flame stabilization and propagation in a PM are governed by the modified Peclet number:

$$Pe = \frac{(\mathbb{S}\_L \ d\_m c\_p \rho)}{k} \tag{1}$$

Numerical Simulation of Combustion in Porous Media 531

**Figure 1.** Schematic of a premixed combustor (M. A. Mujeebu et al. , 2009)

combustion gases raises the solid temperatures from both directions.

For the excess enthalpy combustion, a combustion system using reciprocating flow in PM was introduced. By the reciprocating flow, the combustion gas enthalpy is regenerated into increase in enthalpy of the combustible gas through the PM, which store heat. For this technique a new arrangement of the PM that stabilized flame for a wide operating condition, was used. The mixture first flow in, and the gas and solid temperatures reaches to a maximum at the exit side. Then the flow direction is reversed by means of valves. On the reverse flow half-cycle, the fresh mixture encounters much higher solid temperatures at the entering side. Therefore, the amount of heat recycled becomes larger than that with the single flow direction. Hence in the reciprocating flow system, the heat transfer from the

Production of hydrogen from gases such as methane and hydrogen-sulphide is another potential application of PM combustion. These reactants convert into products such as hydrogen, syngas (H2 and CO), and sulfur. For both methane and hydrogen-sulphide combustion, upstream propagation corresponded to the range of equivalence ratios from stoichiometry to 1.7, and downstream wave propagation was observed for ultra-rich (1.7- 4)

Aluminum oxide (Al2O3), silicon carbide (SiC), and zirconium dioxide (ZrO2) proposed as suitable materials for application. Al2O3 and ZrO2 were recognized as high temperature resistant materials. SiC shows good thermal shock resistance, mechanical strength, and conductive heat transport. SiC also has high melting point (3260 K), against cyclic thermal

**2.3. Reciprocating flow** 

**2.4. Hydrogen production** 

**2.5. Materials for porous media combustion** 

mixtures.

where *SL* is the laminar flame speed, *dm* is the equivalent diameter of the average hollow space of the porous material, *Cp* is the specific heat of the gas mixture, ߩ is the density of the gas mixture and *k* is the thermal conductivity of the gas mixture. For flame propagation through a porous material, the critical Peclet number of 65 has been found. Thus, *Pe < 65* for quenching, and *Pe > 65* for flame propagation.
