Synergistic effects of non-thermal plasma and atomised water injection on NOx reduction in ammonia-based combustion

Ammonia is recognised as a carbon-free energy carrier, yet its combustion is constrained by low reactivity, poor flame stability and high NOx emissions. This study proposes a novel combined approach that integrates non-thermal plasma (NTP) assistance with atomised water injection to simultaneously stabilise ammonia-rich flames and mitigate NOx emissions. One-dimensional chemical kinetics modelling was first employed to assess the feasibility of unassisted NH 3 -air combustion with humidified oxidisers under lean conditions. Experimental investigations were then conducted using a premixed low-swirl burner equipped with a rotating gliding-arc plasma system and a developed ultrasonic water-atomisation module. Lean NH 3 /CH 4 blends were tested with water injections up to 1% by oxidiser mole fraction. The results show that plasma assistance enables stable combustion of ammonia-rich mixtures that would otherwise experience severe slip or blowout. Additionally, plasma-activated water injection decreased NOx emissions by up to 57% at optimal NH 3 /CH 4 ratios, while maintaining flame intensity and stability.