Experiments on Lean Blowout and NOx Emissions of a Premixed Trapped Vortex Combustor With High G-Loading

The feasibility of a novel combustor concept (‘g-load’ combustion with trapped-vortex chamber) to extend the premixed lean-blowout (LBO) limit and to decrease NOx emissions was experimentally determined in a scaled-modular rig that simulated a commercial 250 kilowatt microturbine combustor. The effect of a wide range of g-load’s (770–5050) on the flame regime was identified. The natural gas flame was found to be stabilized in the trapped-vortex cavity (TVC) when the equivalence ratio was within a certain range near the lean blowout limits. The TVC extended the LBO limits to marginally lower mass-based equivalence ratio levels (5%). The LBO limits were found to decrease as the g-loads decrease and the residence time increases, indicating the increase of flame mixing and reaction rates with respect to g-load is not the reason for the extension of LBO limits. The increase of residence time of mixture in the TVC was the reason for the improvement of LBO limits. The new combustor concept would enable operation at lower equivalence ratios, reducing the NOx emissions as much as much as 30%. It also showed that when the flame is contained in the trapped vortex cavity, NOx is reduced compared to baseline combustion concept without TVC.