Abstract
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–ɛ 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.
Highlights
Energy dates back to the beginning of the first human
The initial solution is specified from the results obtained using algebraic model, Eq (4.7)
The normalised mean turbulence kinetic energy profiles for flame F1 are in excellent agreement with the measurements at the centre line for locations close to the nozzle exit, while further down-stream, it is slightly over predicted
Summary
Energy dates back to the beginning of the first human. Primitive man used the wood in the fire for the purpose of heating and cooking. The major challenge in turbulent combustion modelling is due to the interaction of turbulence and chemical reactions This has been studied in the past and these studies, on turbulent premixed flames, are reviewed briefly in the rest of this chapter. Conditional moment closure [27; 40] is an alternative approach showing a good potential to predict minor and pollutant species of engineering interest with moderate computational cost as one shall note from this study. This method has been used widely for non-premixed flames and it is development and application to premixed flames is sparse. The second and third sections focus on CMC for premixed combustion followed by premixed CMC sub-models
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