Streamer polarity dependence of NOx removal by dielectric barrier discharge with a multipoint-to-plane geometry

In this paper, we experimentally investigated an effect of streamer polarity on the reduction of NOx by using a barrier discharge plasma reactor with a multipoint-to-plane geometry. A high-frequency sine wave voltage generator and a repetitive pulse generator, which generated narrow and high-voltage pulses were used to remove nitrogen oxide (NOx). By the optical spectrum measurement, it is clarified that electrons with high energy, more than 10 eV, are produced in the discharge region at atmospheric pressure. The intensity ratio of the first negative system of N-2(+) (391.4 nm, threshold energy 18 eV) to the second positive system of N-2 (337.1 nm, threshold energy 11 eV) neither depends on the applied voltage nor the frequency, but it depends on streamer polarity. Further, it is shown that the value is higher in a positive streamer than in a negative streamer. The use of a multipoint-to-plane electrodes caused the streamer polarity interchange every half cycle of the sine wave of the applied voltage, while in a case of the parallel plane electrodes, the positive streamer was only generated in the discharge region. The simulated gas and the exhaust gas from a diesel engine generator were used to confirm the NOx removal performance of the reactor.