Abstract
A high-power gliding arc (GA) discharge was generated in a turbulent air flow driven by a 35 kHz alternating current electric power supply. The effects of the flow rate on the characteristics of the GA discharge were investigated using combined optical and electrical diagnostics. Phenomenologically, the GA discharge exhibits two types of discharge, i.e., glow type and spark type, depending on the flow rates and input powers. The glow-type discharge, which has peak currents of hundreds of milliamperes, is sustained at low flow rates. The spark-type discharge, which is characterized by a sharp current spike of several amperes with duration of less than 1 μs, occurs more frequently as the flow rate increases. Higher input power can suppress spark-type discharges in moderate turbulence, but this effect becomes weak under high turbulent conditions. Physically, the transition between glow- and spark-type is initiated by the short cutting events and the local re-ignition events. Short cutting events occur owing to the twisting, wrinkling, and stretching of the plasma columns that are governed by the relatively large vortexes in the flow. Local re-ignition events, which are defined as re-ignition along plasma columns, are detected in strong turbulence due to increment of the impedance of the plasma column and consequently the internal electric field strength. It is suggested that the vortexes with length scales smaller than the size of the plasma can penetrate into the plasma column and promote mixing with surroundings to accelerate the energy dissipation. Therefore, the turbulent flow influences the GA discharges by ruling the short cutting events with relatively large vortexes and the local re-ignition events with small vortexes.
Highlights
Non-thermal plasma generated by atmospheric-pressure discharge has great potentials in various applications such as health care, material treatment, pollution controlling, combustion enhancement, transportation, and manufacturing.[1–7] the generation and maintenance of non-thermal plasmas in large power at atmospheric pressure is difficult because they transit to thermal plasmas due to thermal instability or thermionic emission of electrons from the cathode spot.[8]
A high-power gliding arc (GA) discharge was generated in a turbulent air flow driven by a 35 kHz alternating current electric power supply
The spark-type discharge, which is characterized by a sharp current spike of several amperes with duration of less than 1 ls, occurs more frequently as the flow rate increases
Summary
Non-thermal plasma generated by atmospheric-pressure discharge has great potentials in various applications such as health care, material treatment, pollution controlling, combustion enhancement, transportation, and manufacturing.[1–7] the generation and maintenance of non-thermal plasmas in large power at atmospheric pressure is difficult because they transit to thermal plasmas due to thermal instability or thermionic emission of electrons from the cathode spot.[8]. The gliding arc (GA) discharge sustained by an alternating current (AC) power supply was proposed as a simple and low-cost scheme to generate high-power non-thermal plasma at atmospheric pressure.[12–16]. In the GA discharge, the weakly ionized plasma column moves together with the surrounding gases, so the flow field and the plasma are strongly coupled to interact mutually. The flow field can be influenced by the moving plasma through gas heating and arc displacement.[17]. The physical properties of the plasma column change under different flow rates. With the increase in the flow rate, the input power per unit discharge length, the electric field strength along the plasma column, and the impedance of arc column become larger.[18–21]. The attainable maximum discharge length increased 30% with the flow rate varying from 5.4 m/s to 1.6 m/s under certain conditions.[19] With the increase in the flow rate, the input power per unit discharge length, the electric field strength along the plasma column, and the impedance of arc column become larger.[18–21] The attainable maximum discharge length increased 30% with the flow rate varying from 5.4 m/s to 1.6 m/s under certain conditions.[19]
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