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Numerical Study of Reacting Flows in Porous Burners Open Access

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Numerical Study of Reacting Flows in Porous BurnersSustaining combustion within a porous medium is a technology that could potentially improve thermal performance while reducing emissions of gases, such as nitrogen oxides, that are harmful to the environment. Compared to conventional combustion methods, combustion inside the porous burner has advantages such as low emission and large range of firing rate.The objective of the current work is to study combustion in porous burners using a two-dimensional axisymmetric numerical model. Compared with the one-dimensional and two-dimensional numerical models discussed in the existing literature, the two-dimensional model presented in this study can more accurately predict the combustion characteristics of porous burners including flame zone, emission of air pollutants and combustion temperature.The methane/air combustion is modeled using detailed chemical kinetics for precisely predicting flame location and emission of air pollutants. Separate energy equations are used to accurately model the heat transfer in gas phase and solid matrix. Heat transfer between solid and gas is represented by a heat exchange term. The two-dimensional radiative heat transfer in porous media is modeled using the radiative transfer equation (RTE). Finite-volume equations are obtained by formal integration over control volumes surrounding each grid node. Finite-difference equations are solved iteratively for velocity components, pressure correction, gas enthalpy, species mass fractions and solid matrix temperature. The characteristics of the burner are studied numerically under equivalence ratios ranging from 0.5 to 0.7. Twenty-one species are included, involving 55 chemical reactions. The computed NOx is compared with NOx from similar conventional premixed burners and measured nitrogen oxides in porous burners. The computed solid wall temperature profiles are compared with experimental data of similar porous burners. The obtained agreement is fairly good. The present numerical results show that as the equivalence ratio decreases, the reaction zone moves downstream. Moreover, as the flame speed increases, the NOx mole fraction increases.

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