**1. Introduction**

28 Numerical Simulations

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**6. References**

The demand of fossil fuel resources and air pollution are the major problems that caused by using of fuels. In recent years, many researchers have developed new methods for efficient combustion of fuels. Porous media combustion, also known as filtration combustion in a packed bed, due to the interaction between two different phases, solid and gas or liquid. The theory of filtration combustion involves a new type of flame with exothermic chemical reactions during fluid flow in a porous medium. The term 'filtration combustion' was introduced by Russian scientists for combustion of gas flow through porous media. This term does not correspond to western scientific terminology, still it can be found in special literature as a synonym to combustion within porous media (PM). This process facilitates a combustion process with stability in a wide range of reactant fluid velocities, air-fuel ratios, and power density. PM combustion has some unique characteristics. It gives rise to high radiant output, low NOx (Oxides of Nitrogen) and CO (Carbon Monoxide) emissions, high flame speed and higher power density. A porous material means a material with connected voids that flow can easily penetrate through its structure. This technology is different from conventional combustion, with free flame, thin reaction zone and high temperature gradients. Compared to conventional combustion devices, the combustion efficiency of PM burner is reasonably high and better heat transfer from burned gases to unburned mixture, takes place. On the other hand, in PM combustion three modes of heat transfer conduction, convection, and radiation are significant. In addition, there is a better homogenization of temperature across the PM and the significant amount of radiation helps to preheat the incoming air-fuel mixture at upstream. The technique of premixed combustion within PM has been studied and applied to steady combustion with great success. The porous media combustion has proved to be one of the applicable options to solve the problems to a remarkable extent in both technical and economic perspectives. This technique has been used for both gaseous and liquid fuels in steady or unsteady combustion. Flame stability in

© 2012 Ziabasharhagh and Mohammadi, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

PM with lean and rich mixtures, significant reduction in pollutants and increasing combustion efficiency, was proven.

In recent years many researchers investigated the PM combustion technology both experimentally and theoretically. The most of researches are in field of steady combustion in PM and few of them are about transient flame propagation, both approaches are employed in PM combustion. Steady combustion is widely used in radiant burners and surface combustor-heaters due to its high radiant emissivity of the solid. The combustion zone is stabilized by its solid. The other, transient leads to an unsteady reaction zone freely propagate as a filtration combustion wave in the downstream direction. Combustion in PM differs considerably from the homogeneous flames flame front. Considerable features of PM for application of combustion technology are: large specific surface area, excellent heat transfer properties, heat capacity, transparency for fluid flow, thermal resistance, mechanical resistance, recuperation of energy and electrical properties.
