Numerical simulations of a low emission lab-scale burner, referred to as stagnation point reverse flow(SPRF) combustor are performed. The flow features and the combustion characteristics of both premixedand non-premixed modes are studied using large Eddy simulations (LES) using a sub-grid scalar mixingclosure. The computed mean and root mean square (RMS) quantities in both premixed and non-premixedmodes compare well with the corresponding experimental measurements. Computations accurately predictheat release, dilution of hot products with the reactants, entrainment rate of hot products into the fuel andair jets, and in the non-premixed mode, the mixing of fuel and air. Both computations and experimentsshow 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 theinjector, while in the non-premixed mode, flame is lifted from the injector. Results are used to highlightsome of these differences as well as some similarities. It is shown that premixing with hot products isthe process that enables stable operation at a very lean equivalence ratio. In the non-premixed mode, significantpartial mixing of fuel and air before the combustion zone results in combustion close to the premixedmode.
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