Simulation of detailed chemistry in a turbulent combustor flow

Abstract

This paper describes the inclusion of detailed chemical reaction mechanisms in the framework of a turbulent flame simulation. Calculations are based on a finite-volume solution procedure including submodels for turbulent flow, radiative heat transfer, combustion of fuel, and pollutant formation. The interaction of chemical reactions and turbulence is modeled using the eddy dissipation concept (EDC), which has been extended to include detailed chemical reaction mechanisms. For the oxidation of methane, a detailed C1/C2 mechanism is compared with a skeletal mechanism, which is also used to calculate the formation of nitrogen oxide. The basic idea of incorporating the reaction mechanism into the EDC is described. The numerical effort of the resulting coupled partial differential equation system involved investigations of adequate reduction methods. The proposed model is applied to a 400-KW turbulent diffusion methane flame in a cylindrical furnace of which experimental results are available for a detailed evaluation of the proposed method. Predictions are performed with full and skeletal mechanisms. The measured trends in temperature and species concentrations of CH4, O2 CO, CO2 and NO are reproduced adequately by the predicted profiles. Steady-state conditions have been introduced for many of the radical concentrations. In this way, the numerical effort can be lowered considerably without affecting the results compared to calculation without steady state conditions. Postprocessor calculation of the NO chemistry shows some differences compared with the coupled solution. However, considering the uncertainties and simplifications included in a turbulent flame calculation. the postprocessor calculation shows reasonable agreement. Investigations on the mechanisms of NO formation reveal that the calculated thermal NO cannot account for the experimentally observed NO, and prompt NO makes a significant contribution to the NO emission of this flame.