The Effects of Multilayer Porous Media on the Efficiency of Filtration Combustion

Diffusion filtration combustion in a radiative jet burner is numerically investigated. This study focuses on the effects of the porous media structure on the efficiency of nonpremixed combustion, namely combustion temperature and NOx emissions. For this investigation, methane-air combustion within a two-layer porous media is considered. Twodimensional axisymmetric model is chosen to reduce the number of elements and the corresponding computational resource requirements. Fluid turbulence is resolved using the kω SST turbulence model, while the turbulence-controlled reaction rates are computed using the eddy dissipation model. Stoichiometric, two-step methane-air reaction is utilized in the reaction zone. In the present model both thermal and prompt NOx formation mechanisms are considered, where an extended Zeldovich mechanism is used for thermal NOx formation. For high combustion temperatures where radiative heat flux is larger than that of convection and conduction heat transfer rates, radiation becomes the dominant heat transfer mode. To account for the emission and scattering of thermal radiation by the porous media, the Discrete Ordinate model is considered. The relationship between velocity and pressure corrections is calculated using the SIMPLE algorithm. The layered porous zone arrangement is utilized to increase combustion performance due to enhanced fuel-air mixing through increased heat recirculation within the multilayer porous media. Utilizing two layers of equal height, ɛ=0.6 and 0.45, upstream and downstream, respectively increased combustion temperature while decreasing combustion zone and NOx emission. Additionally, the effects of the thickness of each layer on combustion efficiency are studied. Increasing the height of the low porosity downstream region, which effectively decreases the height of the upstream high porosity region, resulted in increased NOx emissions due to higher temperature in the combustion zone. Keywordsnon-premixed, diffusion filtration combustion, methane-air combustion, porous media