Large Eddy Simulation of turbulent combustion in a stagnation point reverse flow combustor using detailed chemistry

For meeting stringent emission restrictions, a modern solution is to operate in or close to the flameless mode. It implies a copious dilution of the reactants with vitiated gas resulting in low oxidant or fuel concentration and consequently low volumetric heat-release rate. On the contrary to traditional flames where heat release is occurring in very thin fronts, the flameless operation lies in the distributed reaction regime. Flameless operation is therefore associated with complex and non-linear interaction between mixing and chemical reactions. In this framework, this paper investigates turbulent combustion in a stagnation point reverse flow combustor and presents one of the first studies combining Large Eddy Simulation and detailed chemistry for capturing the reaction and flow dynamics during flameless combustion. The paper reports a comprehensive sensitivity analysis where the effects of the numerical discretization grid, of the chemical mechanism, of the operation (premixed vs. non-premixed) and of the heat-losses at the walls are studied and compared. Further, the simulation results are compared with experimental data from the literature, giving confidence in the quality of the predictions. The reaction and flow dynamics are extracted from the results using modal analysis, showing rotational and helical structures. Finally, the distribution of intermediate species in the reaction layer is investigated bringing some new insights into the flameless combustion process and providing recommendations for further experimental investigations. (C) 2014 Elsevier Ltd. All rights reserved.