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

The effects of gliding arc discharges on the stability limits of externally perturbed methane/air swirl flames were investigated. The low-frequency flow disturbance mimicking the transient conditions in practical 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 employed to visualize the instantaneous flow and flame structures. Results showed 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 revealed 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 demonstrated that in the presence of gliding arc dis-charges, the flame response to the flow disturbance consists of three stages, i.e., enhancement, extinction, and re-ignition processes. Proper orthogonal decomposition analysis of OH-PLIF images showed a significant 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.