Stabilization of a Turbulent Premixed Flame Using a Nanosecond Repetitively Pulsed Plasma

A nanosecond repetitively pulsed plasma (NRPP) produced by electric pulses of 10 kV during 10 ns at a frequency of up to 30 kHz has been used to stabilize and improve the efficiency of a 25-kW lean turbulent premixed propane/air flame $({\rm Re}_{D} = 30\,000)$ at atmospheric pressure. We show that, when placed in the recirculation zone of the flow, the plasma significantly increases the heat release and the combustion efficiency, thus allowing to stabilize the flame under lean conditions where it would not exist without plasma. Stabilization is obtained with a very low level of plasma power of about 75 W, or 0.3% of the maximum power of the flame. In addition, they find that at high flow rates, where the flame should normally blow out, the NRPP allows the existence of an intermittent V-shaped flame with significant heat release, and at even higher flow rates the existence of a small dome-shaped flame confined near the electrodes that can serve as a pilot flame to reignite the combustor. Optical emission spectroscopy measurements are presented to determine the temperature of the plasma-enhanced flame, the electron number density, and to identify the active species produced by the plasma, namely O, H, and OH.