Experimental investigation on the effects of gliding arc plasma on the combustion characteristics of air stratified NH₃ flames

<p dir="ltr">This study investigates the impact of gliding arc plasma (GAP) on emission characteristics in NH₃-air flames with premixing ratios ranging from 0% to 25% at global equivalence ratios (er of 0.8 and 0.9. The experiments are carried out in a dual swirl burner, where a premixed NH₃-air mixture is introduced through the inner nozzle and central lance for GAP interaction, and non-premixed air is supplied via the outer nozzle. This study is the first to apply gliding arc plasma (GAP) to air-stratified ammonia flames, and this approach provides a significant and novel method for reducing NOx emissions. The results show that GAP reduces NOx emissions by up to 40% under fully non-premixed conditions. At er of 0.8, a critical transition appears when premixed air exceeds 20%, resulting in increased NO emissions. In contrast, for er= 0.9, GAP consistently maintains stable NO reduction across all tested premixing ratios. The spectral analysis of the flame shows that the OH and NH₂ radicals play a pivotal role in mediating the effect of GAP on NO formation. These radicals exhibit competing influences, with NH₂ formation favoured under plasma activation. The NH₂ radical primarily forms through two plasma-driven pathways: O(²D) + NH₃ → OH + NH₂ and N(²D) + NH₃ → NH + NH₂. The observed reduction of NO with plasma is primarily due to the increased production of NH2 related to OH.</p>