About the Development and Dynamics of Microdischarges in Toluene-Containing Air

Ronny Brandenburg,Milko Schiorlin,Michael Schmidt,Sina Jahanbakhsh

doi:10.1007/s11090-019-09971-y

Abstract

The development of microdischarges and the inception dynamics of subsequent microdischarges in an electrode arrangement consisting of a metal pin and a hemispherical dielectric-covered electrode, operated in air with a small toluene admixture, is studied. The discharge is operated with sinusoidal high voltage. A gated ICCD camera and a current probe enable the recording of images and current pulses of the single microdischarges, respectively, while the spatio-temporally resolved development is measured with a multi-dimensional time-correlated single photon counting technique. The overall discharge dynamics changes significantly if a concentration of 35 ppm toluene is added to dry air. A lower high voltage amplitude than in dry air is needed for stable discharge operation. This can be explained by the lower ionization energy of toluene compared to molecular oxygen and nitrogen. The microdischarge development is the same with or without admixture, i.e. a positive (cathode directed) streamer mechanism is observed. Lower mean power is dissipated into the discharge when toluene is admixed. The main effect caused by toluene admixture is the suppression of high-energy microdischarges in case of the cathodic pin half-cycle of the sinusoidal high voltage. The influence on the inception voltage by additional ionization mechanisms and volume memory effects, the consumption of energetic electrons for toluene decomposition reactions, and the modification of the surface by plasma treatment are discussed as possible reasons.

Highlights

Dielectric barrier discharges (DBDs) are an established approach for the generation of ozone and the abatement of air impurities from exhausts and off-gases [1,2,3]
The properties, the inception dynamics and the development of MDs in toluene containing dry air are studied in an asymmetric DBD arrangement consisting of a metal pin and a hemispherical dielectric-covered electrode
The discharge is operated by sinusoidal high voltage with a frequency of 7.5 kHz

Summary

Introduction

Dielectric barrier discharges (DBDs) are an established approach for the generation of ozone and the abatement of air impurities from exhausts and off-gases [1,2,3]. The physics of MDs or single DBDs in air and other nitrogen/oxygen gas mixtures has been studied by experimental methods, in particular electrical measurements [16,17,18,19,20,21,22,23], optical emission spectroscopy and imaging [24,25,26,27,28,29], Streak camera recording [19, 30], time-correlated single photon counting [31,32,33] and laser diagnostics [34,35,36,37] as well as by simulation and modelling [38,39,40,41,42,43,44,45,46]. The variation of the oxygen concentration in argon and nitrogen had a significant impact on the removal efficiency, which was explained by the balances between atomic oxygen generation, its fast reactions with the VOC molecules and the formation of ozone, which is slow reacting with the hydrocarbons. The humidity has an effect on both, the discharge physics and the removal efficiency of VOCs [49]

Results

Discussion

Conclusion