Numerical Investigation of a Stagnation Point Reverse Flow Combustor

Abstract

Flameless combustion is characterized by ultra-low NOx emissions, high combustion efficiency and very stable flame, which is able to operate stably at very lean fuel-air mixtures without problems of combustion oscillation and flashback. Stagnation Point Reverse Flow (SPRF) combustors, as an important application of flameless combustion, have been experimentally studied by various optical diagnostic techniques. In this paper, Eddy Dissipation Concept (EDC) model with detailed chemical reaction mechanisms of natural gas GRI 2.11 is used to investigate the flame characteristics of a SPRF combustor operating at premixed mode with various mass flow rates and equivalence ratios of CH4 and air mixtures. The numerical results indicate that as the fuel and air mixture injection velocities increase, there are no distinct changes in the jet penetrations. However, flame temperatures and NOx emissions decrease, CO emissions increase, and OH is distributed in wider area and more evenly. For turbulent flow, intense reactions take place in the shear layer and the stagnation zone and they gradually shift to the combustor outlet as the jet velocities increase. As the equivalence ratios increase from 0.5 to 1, the NOx emissions always increase, although they are very low when equivalence ratio is below 0.7. However, the CO emissions decrease firstly, reaching the minimum value at equivalence ratio of 0.58, and then increase. The numerical results are compared with experimental data and it is verified that EDC model can capture the important flow field characteristics and flame structure and is appropriate for modeling SPRF combustor.