NRPD-Enabled Swirl-Stabilized Combustor Design for Premixed CH 4 /NH 3 /air: Impact on NO Emissions and Flow Structures

Nanosecond Repetitively Pulsed Discharges (NRPD) have been known to reduce NO in pure ammonia flames at select conditions in different burners. In this paper, we show that these gains extend to CH4/NH3 mixtures as well, including those with low ammonia to methane ratios. In tests in a swirl-stabilized combustor using a pin to surface electrode arrangement for NRPD, we see NO reduction of nearly 200 ppm across the conditions studied. To determine how this electrode assembly can be scaled to larger systems at higher power densities, we study how some key flow structures in the combustor like the recirculation zone are impacted by the presence of the electrodes and the tapered nozzles necessary to create an effective NRPD. We find that in some cases, tapering the post-swirl channel to get a narrow arc-gap eliminates the inner recirculation zone often associated with these swirling flows, and in at least one case, combustion inhibits the vortex breakdown that exists in the non-reacting flow.