EXPERIMENTAL STUDY ON THE EFFECTS OF ROTATING GLIDING ARC PLASMA ON LEAN PREMIXED SWIRLING FLAMES

Plasma-assisted combustion is considered a highly promising combustion control technique with substantial potential to enhance ignition and flame stability performance under extreme conditions. Gliding arc discharge plasma, characterized by its high energy, wide arc coverage, and suitability for high-pressure conditions, presents advantageous features for applications such as ignition and combustion enhancement. In this study, we experimentally investigate the influence of three-dimensional rotating gliding arc (RGA) plasma on lean premixed bluff-body swirling methane/air flames. Firstly, the discharge characteristics were thoroughly examined, including the electrical and spectral properties, the motion and dynamic behavior of the arc column, and thermal effects. Then the structure and flame morphology transition process of swirling methane/air flames were obtained using OH-PLIF (planer laser-induced fluorescence), and the effectiveness of plasma in extending the lean blowoff limits of swirling flames was investigated. Finally, the NO_x emissions in swirling flames were measured using the Gasmet DX4000 FTIR (Fourier Transform Infrared) gas analyzer, with the sampling probe positioned at the outlet of the combustion chamber. The results demonstrate that RGA plasma could generate a substantial number of active radicals, promoting flame chemical chain reactions. Additionally, the overall thermal effects are relatively weak, primarily manifesting as localized heating. The discharge characteristics are closely related to the airflow and applied voltage. RGA plasma could enhance flame stability and extend the lean blow-off limit effectively. This enhancement is primarily attributed to the fact that RGA plasma could serve as an ignition source and flame stabilizer, effectively igniting the mixture and facilitating the formation of an outer recirculation zone flame. Finally, this study reveals that RGA plasma increases NO_x emissions, as NO originates from the plasma. The addition of fuel resulted in a decrease in NO emission in comparison with NO content during the discharge in air. Particularly, RGA plasma leads to a minimum of 65% increase in NO emissions, and NO emissions decrease with decreasing equivalence ratio.