Characteristics of Unsteady Rotating Gliding Arc Induced Ignition of Ammonia-Air Mixture in Swirling Flow

This work investigates the rotating gliding arc (RGA) induced ignition of ammonia -air mixtures by the synchronized measurements of voltage (U), current (I), the snapshots of RGA and ammonia flame, as well as the numerical simulation, focusing mainly on the effects of unsteady characteristics of RGA on ignition. The experimental and numerical results both reveal that the complexity of RGA induced ignition process is closely related to the unsteady discharge powers and positions. In the experiment, two kinds of ignition modes including the anchored flamelet mode and the outwardly propagating flame mode have been classified. A conical flame formed in the central recirculation zone (CRZ) is always necessary to achieve the outwardly propagating flame mode (i.e. a successful ignition). It is found that the adequate power of RGA released near the head of the bluff body can facilitate the formation of the conical flame. The probability to form a conical flame may be reduced as the RGA jump to somewhere apart from the head of the bluff body frequently. The numerical results further reveal that the structure of flow field in the CRZ also has impacts on the formation and propagation of the conical flame. The destruction of the recirculating flow field in the CRZ can destabilize the conical flame to result in a larger local Karlovitz number and a longer ignition delay time. It thus confirms the importance of flow field disturbances resulting from unstable plasma discharges, which may directly affect the formation and propagation of the conical flame.