This study presents the effect of a nanosecond pulsed plasma on premixed methane/air and ammonia/air flames in a model gas turbine dump combustor with an annular swirling flow. A hysteresis phenomenon on blowoff is observed in the study of methane/air flames. Therefore, the lean blowoff limit is not uniquely defined. This hysteresis phenomenon depends on the initial value of the equivalence ratio at which the flame is ignited and the air flow rate. Different methane/air flame morphologies are also observed depending on the equivalence ratio and the region where the flame is stabilized. If a nanosecond pulsed plasma is applied at the combustor nozzle exit, a stable inner shear layer flame is always observed. The lean blowoff limit is significantly extended, and the hysteresis phenomenon disappears with plasma activation. This indicates that plasma provides an additional mechanism for flame stabilization. It is found that plasma activation increases NOx concentration and decreases CO concentration through emission analysis.
Ammonia (NH3) is a carbon-free fuel with high hydrogen content. However, the application of ammonia/air combustion has two significant challenges: high NOx emission and poor flame stability. This study also presents the effects of the nanosecond pulsed plasma on ammonia/air flames to overcome these two challenges. Both lean blowoff limits and NOx emission are investigated in a premixed swirl burner with nanosecond pulsed plasma. With plasma activation, the lean blowoff limits of ammonia flame are extended, and flames are stabilized near the inner shear layer. Emission measurement at the center of the quartz tube exit shows that NOx emissions are significantly reduced with plasma. It is surprising that NOx further decreases with the increase in discharge power and voltage. The tendency of NOx formation is the exact opposite of the results for methane/air flames in the identical setup.