Photographic Investigation of Repetitive Pulsed Discharge Light from Needle Electrode Spraying Water

It is difficult to expand both streamer corona and fine droplets, simultaneously from a syringe needle. In the previous study, we succeeded in the alternate expansion of streamer corona and fine droplets from a syringe needle subjected to the rippled voltage. Electrospray was promoted when the ripple voltage had the frequency component of the natural vibration frequency of the droplet at the tip. In this study, first, the frequency of the rippled voltage was optimized. The existence probability of fine droplets tended to be high (>80%) over a wide phase range (90-180°). Next, a nanosecond pulse was repeatedly superimposed on this rippled voltage at various phases. In the superimposition at a phase where just after the expansion, fine droplet still existed (>80%) between the electrodes, the average discharge light intensity was high. Transient discharge light was observed by using a gated image-intensifier. The streamer from a spraying needle electrode into the gas-liquid two-phase mixing-region reached the lower electrode through the spray area. This result suggests the interaction of streamer corona and fine-droplets, expanded from a syringe needle electrode.