Application of higher-order heat flux model for predicting turbulent methane-air combustion

The present study addresses a new effort to improve the prediction of turbulent heat transfer and NO emission in non-premixed methane-air combustion. In this regard, a symmetric combustion chamber in a stoichiometric condition is numerically simulated using the Reynolds averaged Navier-Stokes equations. The Realizable k-ε model and Discreate Ordinate are applied for modeling turbulence and radiation, respectively. Also, the eddy dissipation model is adopted for predicting the turbulent chemical reaction rate. Zeldovich mechanism is applied for estimating the NO emission. Higher-order generalized gradient diffusion hypothesis (HOGGDH) is employed for predicting the turbulent heat flux in turbulent reactive flows. Results show that the HOGGDH model is capable of predicting temperature distribution in good agreement with the available experimental data. Comparison of the results obtained by the simple eddy diffusivity (SED) and HOGGDH models shows that applying the HOGGDH significantly improves the over-prediction of NO emission. Finally, the average turbulent Prandtl number for the non-premixed methane-air combustion has been calculated.