Role of Electron–Ion Dissociative Recombination in $$\hbox {CH}_{4}$$ Microwave Plasma on Basis of Simulations and Measurements of Electron Energy

Minea, Teofil; Steeg, Alex van de; Wolf, Bram; Silva, A. S. da; Peeters, Floran; Bekerom, D C M van den; Butterworth, Tom; Ong, Qin; Sanden, M.C.M. van de; Rooij, G.J. van

doi:10.1007/s11090-019-10005-w

Cited by 4 publications

(3 citation statements)

References 48 publications

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“…The changing absorbed power density is a likely explanation for this behavior. Alternatively, formation of carbon ions as main charge carrier may become important, which reduces charge recombination losses and consequently again the electron temperature and density [58]. The present diagnostic means do not allow to distinguish these effects unambiguously.…”

Section: Plasma Electron Propertiesmentioning

confidence: 82%

Plasma activation of N₂, CH₄and CO₂: an assessment of the vibrational non-equilibrium time window

Steeg

Butterworth

Bekerom

et al. 2020

Plasma Sources Sci. Technol.

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Vibrational excitation potentially enhances the energy efficiency of plasma dissociation of stable molecules and may open new routes for energy storage and process electrification. Electron, vibrational and rotational temperatures were measured by in situ Thomson and Raman scattering in order to assess the opportunities and limitations of the essential vibration-translation non-equilibria in N2, CO2 and CH4 plasma. Electron temperatures of 1.1–2.8 eV were measured in N2 and CH4. These are used to confirm predominant energy transfer to vibrations after an initial phase of significant electronic excitation and ionization. The vibrational temperatures initially exceed rotational temperatures by almost 8000 K in N2, by 900 K in CO2, and by 300 K in CH4. Equilibration is observed at the 0.1 ms timescale. Based on the vibrational temperatures, the vibrational loss rates for different channels are estimated. In N2, vibrational quenching via N atoms is identified as the dominant equilibration mechanism. Atomic nitrogen population reaches a mole fraction of more than 1%, as inferred from the afterglow emission decay, and explains a gas heating rate of 25 K μs−1. CH4 equilibration at 1200 K is predominantly caused by vibrational-translational relaxation in CH4–CH4 collisions. As for CO2, vibrational-translational relaxation via parent molecules is responsible for a large fraction of the observed heating, whereas product-mediated VT relaxation is not significantly contributing. It is suggested that electronic excitation, followed by dissociation or quenching contributes to the remaining heat generation. In conclusion, the time window to profit from vibrational excitation under the present conditions is limiting practical application.

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Section: Plasma Electron Propertiesmentioning

confidence: 82%

Plasma activation of N₂, CH₄and CO₂: an assessment of the vibrational non-equilibrium time window

Steeg

Butterworth

Bekerom

et al. 2020

Plasma Sources Sci. Technol.

View full text Add to dashboard Cite

show abstract

“…Despite this, the assumption of uniform power deposition and temperature in the discharge may result in significant errors in this calculation, plus there is the possibility of other reaction mechanisms that reduce the electron temperature [64]. These errors preclude definitive statements regarding energy transfer in the plasma, rather these observations provide additional evidence for determining the important heating mechanisms.…”

Section: Microwave Power Transfer and Dissipationmentioning

confidence: 98%

“…uniform plasma power deposition, a Maxwellian distribution of electron energy), propagation of relative large errors (e.g. uncertainty in plasma volume, uncertainty in cross sectional data-particularly for electronic excitation of CH 4 ), or the presence of other species besides CH 4 that may modify the plasma chemistry [64].…”

Section: Microwave Power Transfer and Dissipationmentioning

confidence: 99%

Plasma induced vibrational excitation of CH₄—a window to its mode selective processing

Butterworth

Steeg

Bekerom

et al. 2020

Plasma Sources Sci. Technol.

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Vibrational excitation of methane is believed to promote chemistry and improve product selectivity, compared to thermal conversion methods. We report on unique direct measurements of vibrational–rotational non-equilibrium in methane plasma. The non-equilibrium is sustained for 50 μs, after which the gas temperature equilibrates with the vibrational temperature at around 900 K. The plasma is generated by applying 200 μs, 30 Hz pulses of microwave radiation to methane at 25 mBar. We demonstrate that in microwave discharges, power transfer to vibrational modes of CH4 is the dominant power transfer mechanism, which leads to creation of a vibrational–translational (VT) non-equilibrium. VT relaxation is determined to be the dominant translational heating mechanism in the discharge. However, the high electron temperature at breakdown also leads to strong electronic excitation which may be responsible for some of the heating. Furthermore, we find that the CH4 vibrational levels are in equilibrium with each other due to fast intra-polyad relaxation (VV), and therefore bending vibrational modes population density is greatly in excess of stretching vibrational modes. The window of opportunity to exploit this non-equilibrium is limited by the VT relaxation timescale, which is approximately 50 μs in our experiment.

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Two-Temperature Chemical Non-equilibrium Modeling of Argon DC Arc Plasma Torch

Sun

Zhang

et al. 2020

Plasma Chem Plasma Process

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Role of Electron–Ion Dissociative Recombination in $$\hbox {CH}_{4}$$ Microwave Plasma on Basis of Simulations and Measurements of Electron Energy

Cited by 4 publications

References 48 publications

Plasma activation of N₂, CH₄and CO₂: an assessment of the vibrational non-equilibrium time window

Plasma activation of N₂, CH₄and CO₂: an assessment of the vibrational non-equilibrium time window

Plasma induced vibrational excitation of CH₄—a window to its mode selective processing

Two-Temperature Chemical Non-equilibrium Modeling of Argon DC Arc Plasma Torch

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Role of Electron–Ion Dissociative Recombination in $$\hbox {CH}_{4}$$ Microwave Plasma on Basis of Simulations and Measurements of Electron Energy

Cited by 4 publications

References 48 publications

Plasma activation of N2, CH4and CO2: an assessment of the vibrational non-equilibrium time window

Plasma activation of N2, CH4and CO2: an assessment of the vibrational non-equilibrium time window

Plasma induced vibrational excitation of CH4—a window to its mode selective processing

Two-Temperature Chemical Non-equilibrium Modeling of Argon DC Arc Plasma Torch

Contact Info

Product

Resources

About

Plasma activation of N₂, CH₄and CO₂: an assessment of the vibrational non-equilibrium time window

Plasma activation of N₂, CH₄and CO₂: an assessment of the vibrational non-equilibrium time window

Plasma induced vibrational excitation of CH₄—a window to its mode selective processing