Laser induced fluorescence investigation of the chemical impact of nanosecond repetitively pulsed glow discharges on a laminar methane-air flame

This paper reports on an experimental investigation of the chemical impact of nanosecond repetitively pulsed (NRP) glow discharges on a laminar methane-air flame. The chosen configuration was a lean wall stabilized flame where NRP discharges were generated across the flame front. After careful selection of the excitation lines, planar laser induced fluorescence of OH and CH was conducted. Comparisons between the OH and CH fluorescence of a base flame (without plasma actuation), and those obtained during the steady state and the transient regimes of plasma actuation, were performed. First it is shown that during the steady state regime, the intensity of OH and CH fluorescence in the flame could be increased by up to 40% and 10%, respectively. In addition, the life time of OH fluorescence in the discharge channel was estimated to be between 3 and 4.5 µs. The transient regime at the beginning of plasma actuation showed that the flame began to be affected by the discharges long before OH fluorescence could be detected in the discharge channel, upstream of the flame. After 40 ms of plasma actuation, OH intensity began to increase simultaneously in both the flame and the discharge area. Based on current knowledge of nanosecond discharge chemistry, explanations for these results are proposed.