Plasma-assisted stabilization of premixed swirl flames by gliding arc discharges ?

This paper presents key effects of gliding arc discharges on the stability limits of externally perturbed methane/air swirl flames. The low-frequency flow disturbance mimicking the transient conditions in prac-tical combustor was generated by a flow pulsation system with repetition of ?5 Hz. The synchronized OH planar laser-induced fluorescence and particle imaging velocimetry (OH-PLIF/PIV) measurements were uti-lized to visualize the instantaneous flow and flame structures. We find that, with gliding arc discharges, the lean blowout limits in perturbed flames are dramatically extended by up to 60%, which is more pronounced than in non-perturbed flames. OH-PLIF/PIV results show that, the stabilization effect can be explained by the expansion of the inner recirculation zone, wherein the opening angle increases from 52 ? to 62 ? due to the plasma enhancement. Time-resolved OH-PLIF images illustrate that, in the presence of gliding arc dis-charges, the flame response to the flow disturbance consists of three stages, including enhancement, extinc-tion, and re-ignition processes. Furthermore, proper orthogonal decomposition (POD) analysis of OH-PLIF images reveals a considerable increase of mean energy contents and suppression of turbulent fluctuations. It suggests that the enhancement of gliding arc discharges is not a simple superposition of the energy deposit, but a strong non-linear coupling between the plasma and the turbulent flame with closed-loop feedbacks. ? 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.