Title: Time-resolved in situ measurements and predictions of plasma-assisted methane reforming in a nanosecond-pulsed discharge

Abstract

This study investigates the plasma properties and chemical kinetics of plasma-assisted methane reforming in a He diluted nanosecond-pulsed plane-to-plane dielectric barrier discharge (ns-DBD) through the combination of time-resolved in situ laser diagnostics and a 1-D numerical model. Plasma-assisted fuel reforming kinetic mechanisms have predominantly been evaluated on the basis of matching reactant conversion and syngas production to steady-state measurements, which cannot describe the full range of chemistry and physics necessary to validate the model. It was found that adding 1% CH₄ to a pure He ns-DBD led to a faster breakdown along the rising edge of the applied voltage pulse, thereby lowering the reduced electric field (E/N), electron number density, and electron temperature. Further addition of CH₄ did not continue to alter the E/N in the model. Laser absorption spectroscopy was used to measure gas temperature, C₂H₂, H₂O, and CH₂O in a CH₄/CO₂/He discharge to serve as validation targets for the predicted reaction pathways. CH₂O was predicted within 25% of the measured value, while H₂O and C₂H₂ were under-predicted by a factor of two and three, respectively. From path flux analysis, the major pathway for CH₂O formation was through the reaction between CH₃ and O, while C₂H₂ formation had multi-step pathways that relied on ions like CH$$^{+}_{3}$$ and C₂H$$^{+}_{5}$$. The path flux analysis also shows that CH₂ is a significant intermediate for production of both CH₂O and C₂H₂, and increased CH₂ concentration could improve model predictions. The results show that the use of reaction rate constants with lower uncertainties and inclusion of He$$^{+}_{2}$$, are needed to improve the predictions. Lastly, varying the ”equivalence ratio”, defined by the CH₄ dry reforming reaction to H₂ and CO, from 0.5 to 2 was shown to have a weak effect on measured product species and experimental trends were explained based on pathways extracted from the model.

Authors:

Chen, Timothy Y.  ^[1];

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• Search DOE PAGES for ORCID "0000-0003-3026-9767"

Taneja, Taaresh S.  ^[2];

• Search DOE PAGES for author "Taneja, Taaresh S."
• Search DOE PAGES for ORCID "0000-0002-0233-2039"

Rousso, Aric C.  ^[1];

• Search DOE PAGES for author "Rousso, Aric C."
• Search DOE PAGES for ORCID "0000-0002-5710-3233"

Yang, Suo  ^[2];

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• Search DOE PAGES for ORCID "0000-0002-9924-2645"

Kolemen, Egemen  ^[1];

• Search DOE PAGES for author "Kolemen, Egemen"
• Search DOE PAGES for ORCID "0000-0003-4212-3247"

Ju, Yiguang ^[1]

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+ Show Author Affiliations

1. Princeton Univ., NJ (United States)
2. Univ. of Minnesota-Twin Cities, Minneapolis, MN (United States)

Publication Date:

Sat Sep 26 00:00:00 EDT 2020

Research Org.:

Princeton Univ., NJ (United States)

Sponsoring Org.:

USDOE

OSTI Identifier:

1906177

Alternate Identifier(s):

OSTI ID: 1777033

Grant/Contract Number:  

SC0020233

Resource Type:

Accepted Manuscript

Journal Name:

Proceedings of the Combustion Institute

Additional Journal Information:

Journal Volume: 38; Journal Issue: 4; Journal ID: ISSN 1540-7489

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Non-equilibrium plasma; Plasma assisted fuel reforming; Chemical kinetics; Methane dry reforming; Pyrolysis