Non-Premixed CH₄ Combustion in a Porous Medium

Combustion process is the major contributor to the air pollution, such as CO, unburned hydrocarbon, soot and NO_x, etc. Porous media can be a good candidate for improving the combustion efficiency and reducing pollution formation. Premixed combustion has been extensively investigated in the literature, experimentally and computationally. However, investigation of non-premixed combustion in porous media is limited in the open literature, which is the topic of this paper. The present work deals with the numerical modeling of methane/air non-premixed combustion in porous media. Physical problem that is considered here is fuel jet which is injected to the air in free flame case and injected into a porous medium, in the porous medium combustion case. The flow is assumed turbulent and standard k-ε model with standard wall functions is used in the simulation. The solid porous structure is assumed to be composed of alumina fiber material with temperature dependent heat conductivity. Discrete Ordinate method is used to solve radiative transport equations. The governing equations are solved using finite volume method. The results show that the combustion in porous media has superior combustion efficiency and significantly lower NO_x and CO emissions compare to the free flame. This is due to the lower maximum temperature in porous media combustion. In comparison with the free flame case where the combustion zone is narrow and long, the results shows the combustion zone in porous media is shorter in axial and wider in radial direction.