Rotating gliding arc discharge induced flame oscillation near the lean blowout limit

This work investigates the rotating gliding arc (RGA) assisted swirling methane combustion characteristics near the lean blowout limit by utilizing the high-speed videography. As the flow rate and the global equivalence ratio were varied, four flame modes, namely self-sustained flame, RGA-sustained stable flame, RGA-induced oscillating flame, and RGA anchored flame modes were detected. In particular, the oscillating flame mode with an oscillating frequency of 2∼4 Hz occurs with the air flow rates above 13 L/min and the equivalence ratio between 0.52 and 0.56. It is an RGA-induced low-frequency flame oscillation phenomenon. The RGA discharge characteristics can impact the oscillating behaviors that with the increase of the transformer input voltage, the flame oscillation frequency is enhanced and the averaged flame area becomes larger to result in a higher combustion efficiency. Besides, increasing the wall temperature of the combustion chamber promotes the combustion during the oscillating stage. Based upon the experimental and numerical results this RGA-induced low-frequency oscillating flame are further interpreted by a three-staged mechanism. It implies that the first stage, during which the fuel/oxidant mixture is refreshed in the chamber and the temperature increases through recirculating flow gradually, determines the oscillating frequency. The fast accumulation of released energy from plasma discharge and partial fuel burning by recirculation can accelerate the temperature growth in the recirculation zone to increase the oscillation frequency. In all, this unique oscillating phenomenon and related explanations indeed broaden our knowledge of oscillating combustion behaviors and GA assisted combustion.