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Conditional Moment Closure (CMC) is a suitable method for predicting scalars such as carbon monoxide with slow chemical time scales in turbulent combustion. Although this method has been successfully applied to non-premixed combustion, its application to lean premixed combustion is rare. In this study the CMC method is used to compute piloted lean premixed combustion in a distributed combustion regime. The conditional scalar dissipation rate of the conditioning scalar, the progress variable, is closed using an algebraic model and turbulence is modelled using the standard k-ε model. The conditional mean reaction rate is closed using a first order CMC closure with the GRI-3.0 chemical mechanism to represent the chemical kinetics of methane oxidation. The PDF of the progress variable is obtained using a presumed shape with the Beta function. The computed results are compared with the experimental measurements and earlier computations using the transported PDF approach. The results show reasonable agreement with the experimental measurements and are consistent with the transported PDF computations. When the compounded effects of shear-turbulence and flame are strong, second order closures may be required for the CMC.

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The pollutants produced by the burning of fossil fuels have a severe impact on the environment and on mankind. Computational Fluid Dynamics (CFD) is a powerful tool which is widely used to predict the emission of these pollutants from industrial combustion systems. Nevertheless, to predict these emissions the chemical reaction must be represented by a detailed mechanism which include pollutant formation pathways. Thus, using a complex mechanism, especially in 3D simulations with a realistic geometry is prohibitively expensive computationally. In this paper, the Equivalent Reaction Networks (ERN) method is used in conjunction with a ReynoldsAveraged Navier Stokes (RANS) approach to reduce the cost of these computations. For this purpose, a pilot stabilised stoichiometric methane-air flame is chosen with a specific interest in species with slow time scales such as CO and NO x . The Favre averaged CFD results are then compared to previously-reported experimental measurements and earlier computations using Conditional Moment Closure (CMC) at five axial locations within the flame. Despite the simplicity of the ERN method in contrast with other more complex combustion models, the comparison of the CFD results with the experimental measurements for the prediction of CO are extremely encouraging.

In turbulent premixed flames, for the mixing at a molecular level of reactants and products on the flame surface, it is crucial to sustain the combustion. This mixing phenomenon is featured by the scalar dissipation rate, which may be broadly defined as the rate of micro-mixing at small scales. This term, which appears in many turbulent combustion methods, includes the Conditional Moment Closure (CMC) and the Probability Density Function (PDF), requires an accurate model. In this study, a mathematical closure for the conditional mean scalar dissipation rate, <Nc|ζ>, in Reynolds, Averaged Navier–Stokes (RANS) context is proposed and tested against two different Direct Numerical Simulation (DNS) databases having different thermochemical and turbulence conditions. These databases consist of lean turbulent premixed V-flames of the CH4-air mixture and stoichiometric turbulent premixed flames of H2-air. The mathematical model has successfully predicted the peak and the typical profile of <Nc|ζ> with the sample space ζ and its prediction was consistent with an earlier study.