Influence of pulsed gas injections on the stability of Townsend dielectric barrier discharges in nitrogen at atmospheric pressure

Abstract

This work investigates the effects of pulsed nitrogen gas injections on the stability of Townsend dielectric barrier discharges operated in continuous nitrogen gas flows at atmospheric pressure. For single-pulse injections with pulse durations lower than the continuous gas residence time (∼50 ms), current-voltage characteristics reveal homogeneous discharges with a single current peak per half-cycle of the applied voltage. However, a sudden decrease of the discharge power over time combined with a temporary transition from homogeneous to filamentary discharge is observed for longer pulses at fixed pulsed gas flows and for higher pulsed gas flows at fixed pulse duration. In addition, for multiple pulsed gas injections with repetition frequencies between 0.1 and 10 Hz, discharge destabilisation increases with the number of pulses. Time-resolved optical emission spectroscopy reveals that, over the single pulse time scale, temporal variations of the emission intensities are longer than the expected residence times of the continuous and pulsed gas flows. Furthermore, a rise of oxygen impurities can be seen over both single and multiple-pulses time scales. Two-dimensional gas flow simulations reveal that pulsed injections introduce sharp and narrow temporal gas velocity profiles over the range of experimental conditions investigated, with no cumulative effects in the discharge cell from one pulse to the other. However, pulsed operation introduces significant changes in the neutral gas composition with time scales comparable to those revealed by electrical and optical diagnostics. In such conditions, the outgassing of impurities adsorbed on surfaces located upstream of the discharge cell plays a vital role in Townsend discharges’ physics and characteristics.