Novel strategy for combustion enhancement of NH3-air mixture using gliding arc plasma

Abstract

This study investigates the impact of gliding arc plasma (GAP) on the stability and emissions characteristics of a partially premixed ammonia (NH₃)-air swirling flames for wide ranges of global equivalence ratios (ϕ_g). A novel dual-swirl GAP combustor, incorporating conical central electrode serving as a bluff body, is used to generate a rotating gliding arc plasma within the fuel lance. The plasma power is maintained below 1.4 % of the thermal power of the flame across all experimental conditions. This is the first study to apply GAP directly to the fuel side, facilitating premixing immediately after plasma interaction. The results reveal that plasma significantly enhances lean and rich blowout limits by 15–20 % and 30–35 %, respectively. This is mainly due to the continuous local ignition effect through heating and the generation of active species pools. Plasma actuation also results in a substantial reduction in NO and NO₂ emissions, decreasing by 40–80 % and 30–50 %, respectively, depending on ϕ_g in the range of 0.76 to 1.05. Simultaneously, OH* and NH₂* intensities increase by 30–60 % and 70–80 %, respectively. This could indicate an increased NH₂ production favouring NO consumption reactions. A notable NH₃ slip occurs at ϕ_g values exceeding 0.93 and 0.76, indicating incomplete combustion. Numerical results suggest that NO formation predominantly occurs via the HNO pathway, and that plasma conditions promote thermal De-NO_x reactions, notably through NH₂ + NO → NNH + OH and NH₂ + NO → N₂ + H₂O reactions. This study provides critical insights into the potential of GAP technique for advancing NH₃ combustion technologies, offering promising applications for sustainable energy systems.