Effects of gliding arc plasma on lean blow-off and transient ignition characteristics of turbulent premixed and non-premixed swirling flames

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This paper investigates the effects of gliding arc (GA) plasma applied at various positions on the lean blow-off (LBO) performance and transient ignition characteristics of turbulent premixed and non-premixed flames in a laboratory-scale swirl combustor. To enhance the ignition process and extend the limits of flammability and stability, gliding arc plasma, powered by an alternating current (AC) source, is introduced into the inner recirculation zone (IRZ) or outer recirculation zone (ORZ) via either a pin-to-pin or pin-to-plate arc discharge configuration. The electrical and spectral properties of the plasma are characterized, and plasma temperatures are determined using optical emission spectroscopy (OES) diagnostic techniques. The GA plasma ignition process is recorded using high-speed CCD imaging. Additionally, flame structure and stability modes at various equivalence ratios are investigated using digital imaging and CH* chemiluminescence measurements. The results indicate that the GA discharge exhibits highly non-equilibrium plasma characteristics, with elevated vibrational and rotational temperatures, demonstrating strong localized thermal effects and non-thermal chemical effects. The plasma ignition process could be divided into three phases: plasma-induced flame kernel formation, flame propagation and development, and flame stabilization. For both premixed and non-premixed flames, optimal ignition performance is observed at discharge positions A and E, respectively. GA plasma applied in the IRZ significantly extends the LBO limits. However, plasma applied in the ORZ could not affect the stability mode or LBO limits, indicating that under the experimental conditions of this study, the application of AC-powered GA plasma in the ORZ is not an effective strategy.