Discharge and emission characteristics of rotating gliding arc plasma using air, ammonia, and ammonia/air mixtures

Owing to the application limitations of ammonia as a clean energy source, plasma-assisted combustion technology has become an effective method for improving the ammonia combustion performance. In this study, the discharge characteristics of a rotating gliding arc (RGA) plasma in air, ammonia (NH₃), and mixed ammonia/air gases were investigated, as well as their effects on combustion and emissions. Studies have shown that increasing the RGA plasma power enhances the stability of the gas discharge voltage and current waveforms, promotes the combustion reaction of mixed gas, and shortens the flame when a high ammonia content is present. In the ammonia discharge spectrum, NH, N₂, H_α, and H_β were primarily observed, whereas in the air discharge spectrum, NO, N₂, OH, and O were mainly observed. The discharge spectrum of the mixed gas containing 10% ammonia was mainly composed of substances common to both discharges, with the intensity of the OH emissions significantly increasing as the power increased. Under varying ammonia concentrations and discharge power conditions, the introduction of the RGA plasma extended the combustion range of ammonia from 20%–25% to 15%. When the ammonia content was low (less than 15%), the NO generated by the air discharge was reduced owing to the reduction reaction of ammonia. When the ammonia content exceeded 15%, the NO concentration increased with increasing power. When the discharge power was less than 10% of the combustion power (power ratio), the NO produced was either less than or comparable to the NO generated by ammonia combustion without plasma. However, when the power ratio exceeded 10%, the combustion reaction was enhanced, leading to a sharp increase in NO emissions. The combustion reaction temperature of the mixture increased steadily as the power increased. These findings offer valuable insights into optimizing the plasma-assisted ammonia combustion process, enhancing the combustion efficiency, and minimizing pollutant emissions, thereby improving environmental sustainability.