LES of premixed and non-premixed combustion in a stagnation point reverse flow combustor

Numerical simulations of a low emission lab-scale burner, refer-red to as stagnation point reverse flow (SPRF) combustor are performed. The flow features and the combustion characteristics of both premixed and non-premixed modes are studied using large Eddy simulations (LES) using a sub-grid scalar mixing closure. The computed mean and root mean square (RMS) quantities in both premixed and non-premixed modes compare well with the corresponding experimental measurements. Computations accurately predict heat release, dilution of hot products with the reactants, entrainment rate of hot products into the fuel and air jets, and in the non-premixed mode, the mixing of fuel and air. Both computations and experiments show that the velocity field in both SPRF modes are qualitatively similar in the second half of the combustor. However, the heat release zones are quite different. In the premixed mode, flame is attached to the injector, while in the non-premixed mode, flame is lifted from the injector. Results are used to highlight some of these differences as well as some similarities. It is shown that premixing with hot products is the process that enables stable operation at a very lean equivalence ratio. In the non-premixed mode, significant partial mixing of fuel and air before the combustion zone results in combustion close to the premixed mode. (C) 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.