Optical diagnostics of a gliding arc

Abstract

Dynamic processes in a gliding arc plasma generated between two diverging electrodes in ambient air driven by 31.25 kHz AC voltage were investigated using spatially and temporally resolved optical techniques. The life cycles of the gliding arc were tracked in fast movies using a high-speed camera with framing rates of tens to hundreds of kHz, showing details of ignition, motion, pulsation, short-cutting, and extinction of the plasma column. The ignition of a new discharge occurs before the extinction of the previous discharge. The developed, moving plasma column often short-cuts its current path triggered by Townsend breakdown between the two legs of the gliding arc. The emission from the plasma column is shown to pulsate at a frequency of 62.5 kHz, i.e., twice the frequency of the AC power supply. Optical emission spectra of the plasma radiation show the presence of excited N₂, NO and OH radicals generated in the plasma and the dependence of their relative intensities on both the distance relative to the electrodes and the phase of the driving AC power. Planar laser-induced fluorescence of the ground-state OH radicals shows high intensity outside the plasma column rather than in the center suggesting that ground-state OH is not formed in the plasma column but in its vicinity.

In-Situ Non-intrusive Diagnostics of Toluene Removal by a Gliding Arc Discharge Using Planar Laser-Induced Fluorescence

“…The distance of the laser sheet to the Teflon plate was kept at 9 cm, same as for toluene PLIF. A hollow structure is obviously shown both in the cases with and without toluene which has also been observed in our previous work [10,25]. OH PLIF images presented in Fig.…”

“…2b. The emissions of the discharge channel were mainly from N 2 * [25]. It demonstrated that the non-equilibrium discharge has a string-like channel.…”

“…1, the experimental setup consisted of two parts: the gliding arc system and the PLIF measurement system. The gliding arc discharge system used here was similar to the one used in our previous works [10,25,26] and only a brief description is given here. Two internally water-cooled, diverging stainless steel electrodes were fixed on a Teflon plate, as shown by the inserted direct image in Fig.…”

Translational, rotational, vibrational and electron temperatures of a gliding arc discharge

“…Substantial progress in studying gliding arc discharges has been achieved, including transient discharge processes [30,31], electrical characteristics [32,33], hypergravity effects [34,35] and species distributions [36][37][38], as well as the rotational and vibrational temperatures of gliding arc discharges [25][26][27][28]. However, the translational temperature of the gliding arc discharge has not been directly measured yet up to now.…”

Measurements of 3D slip velocities and plasma column lengths of a gliding arc discharge

“…5,6 Such gliding arc discharges have been widely applied to pollution control, 7-11 surface treatment, 1,12 sterilization, 13 and combustion enhancement. 14 Extensive studies have been performed on the dynamics, [15][16][17][18] physical characteristics, [19][20][21][22][23][24][25][26][27][28] and chemical mechanisms [29][30][31] involved in gliding arc discharges. Phenomenological models 21,[32][33][34] were developed to explain the discharge behavior based on accurate measurements of several important parameters, including the slip velocityṼ S (it stands for the relative velocity between the plasma columnṼ C and the gas flowṼ F , and its magnitude is jṼ S j ¼ jṼ C ÀṼ F j), and the length of the plasma column.…”