Dynamic response of a weakly turbulent lean-premixed flame to nanosecond repetitively pulsed discharges

We report on an experimental study of the temporal response of a 2-kW bluff-body stabilized weakly turbulent lean-premixed propane-air flame when applying Nanosecond Repetitively Pulsed (NRP) discharges. NRP discharges are created by voltage pulses of amplitude 10 kV, duration 10 ns, applied at a frequency of up to 80 kHz between two pin electrodes placed in the recirculation zone downstream of the bluff-body. The averaged electrical power deposited by the plasma is up to 20 W, or less than 1% of the thermal power of the flame. CH^- chemiluminescence images are recorded starting from the time of the discharge initiation. OH laser induced fluorescence (LIF) measurements have been performed to visualize the location of the burned gases and the chemical activation resulting from NRP discharges. Optical emission spectroscopy (OES) measurements are conducted to determine the temperature in the recirculation zone created by the bluff-body, with and without plasma. The time resolved images show a significant reduction in lift-off height after applying the NRP discharges. This transition occurs within 5 ms of plasma initiation. Taking into account the thermal, chemical and hydrodynamical effects of the NRP discharges, an explanation for the reduction in lift-off height and the associated time scale is proposed.