Study of Non-Thermal DC Arc Plasma of CH₄/Ar at Atmospheric Pressure Using Optical Emission Spectroscopy and Mass Spectrometry

Abstract

Non-thermal C/H/Ar plasmas are widely applied to carbonaceous material production and processing. In this work, plasma parameters and gaseous species of the atmospheric non-thermal C/H/Ar plasmas produced by an atmospheric-pressure DC arc discharge generator in CH4/Ar were investigated. The voltage-current characteristics were measured for different CH4/Ar ratios. Optical emission spectroscopy was employed to analyze the electron excitation temperature, gas temperature and electron density under various discharge conditions. The hydrocarbon molecules produced in the CH4/Ar plasmas were detected with photoionization mass spectrometry. The optical spectral results demonstrated that the electron excitation temperature was 0.4-1 eV, the gas temperature was 2800-4200 K and the electron density was in the range of (5-20)×10 15 cm −3. The mass spectrum indicated that a variety of unsaturated hydrocarbons (C2H4, C3H6, C6H6, etc.) and several highly unsaturated hydrocarbons (C4H2, C5H6, etc.) were produced in the non-thermal arc plasmas.

Detecting trace methane levels with plasma optical emission spectroscopy and supervised machine learning

“…Liao et al observed a large number of C x H y (x 10, y 12) fragment mass peaks from a DC arc Ar-CH 4 plasma operating at a gas temperature >2800 K and at a high CH 4 concentration ( 2%). They also obtained emission spectra but the only molecular derived features observed were weak CH(A-X) and H β lines and stronger lines representing H α and C 2 swan systems [21]. Therefore, we can expect trace methane in our plasma to remain predominantly in molecular form, with dissociated fragments at sub-ppm concentrations.…”

Spectroscopic diagnosis of plasma in atmospheric pressure negative pulsed gas-liquid discharge with nozzle-cylinder electrode

“…The 2λ method (i.e. the relative intensity ratio of two spectral lines) was used to calculate the T e in non-thermal plasma [ [21][22][23][24]. The T e can be deduced from the relation between two excitation levels of O atoms by equation (1).…”

Study of plasma parameters and gas heating in the voltage range of nondischarge to full‐discharge in a methane‐fed dielectric barrier discharge

“…Also, it provides an estimation of the vibrational temperature of species and background gas temperature based on the rotational branch of spectral lines and information relating to the plasma chemistry and substances present in the plasma [26] . Optical emission diagnosis of methane plasma has intensively been investigated in the literature [27][28][29][30][31] . Bai et al studied the reaction mechanism in nonthermal plasma-assisted methane conversion performed by different sources [27] .…”