Actuation efficiency of nanosecond repetitively pulsed discharges for plasma-assisted swirl flames at pressures up to 3 bar

This study analyzes different strategies of plasma actuation of premixed swirl flames at pressures up to 3 bar. A wide range of applied voltages and pulse repetition frequencies (PRF) is considered, resulting in different combinations of nanosecond repetitively pulsed (NRP) discharge regimes, NRP glow and NRP spark discharges. Electrical characterization of the discharges is performed, measuring voltage and current, and deposited energy and power are evaluated. The effectiveness of the plasma actuation is assessed through images of OH* chemiluminescence from the flame. From these images, the distance of the center of gravity of the flame to the burner plate is evaluated, with and without plasma actuation. The results show that strategies which involve a high percentage of NRP sparks are effective at improving flame anchoring at atmospheric pressure, while they are detrimental at higher pressures. Therefore, high applied voltage and low PRF are preferable at atmospheric pressure, while the opposite is observed at elevated pressures. Moreover, it is found that a ratio of plasma power to thermal power of the flame around 1% is the best compromise between a strong actuation of the flame and a reasonable deposited electrical power. Explanations for these results are proposed.