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Natural gas associated with oil wells and natural gas fields is a significant source of greenhouse gas emissions and airborne pollutants. Flaring of the associated gas removes greenhouse gases like methane and other hydrocarbons. The present study explores the possibility of enhancing the flaring of associated gas mixtures (C1 – C4 alkane mixture) using nanosecond pulsed non-equilibrium plasma discharges. Starting with a detailed chemistry for C0 – C4 hydrocarbons (Aramco mechanism 3.0 – 589 species), systematic reductions are performed to obtain a smaller reduced mechanism (156 species) yet retaining the relevant kinetics of C1 – C4 alkanes at atmospheric pressure and varying equivalence ratios (φ = 0.5 – 2.0). This conventional combustion chemistry for small alkanes is then coupled with the plasma kinetics of CH4, C2H6, C3H8, and N2, including electron-impact excitations, dissociations, and ionization reactions. The newly developed plasma-based flare gas chemistry is then utilized to investigate repetitively pulsed non-equilibrium plasma-assisted reforming and subsequent combustion of the flare gas mixture diluted with N2 at different conditions. The results indicate an enhanced production of hydrogen, ethylene and other species in the reformed gas mixture, owing to the electron-impact dissociation pathways and subsequent H-abstractions and recombination reactions, thereby resulting in a mixture of CH4, H2, C2H4, C2H2, and other unsaturated C3 species. The reformed mixture shows an enhanced reactivity as exhibited by their shorter ignition delays. The reformed mixture is also observed to undergo increased methane destruction and higher equilibrium temperatures compared to the original mixture as the gas temperature increases, thereby exhibiting a potential for reducing the unburnt emissions of methane and other hydrocarbons.
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Evaluating the role of product gas composition in vibrational relaxation in pulsed microwave plasma-enhanced flames
Hybrid fs/ps coherent anti-Stokes Raman scattering (CARS) is employed to investigate the vibrational temperature evolution of N2 in lean methane flames exposed to pulsed microwave irradiation. Vibrational temperature during and post microwave illumination by a 2 μs, 30 kW peak power, 3.05 GHz pulse is monitored in flames diluted with N2, N2 and CO2 , and N2 and Ar. Electric field strengths inside the microwave cavity are monitored directly using electric field probes. Temperature increases up to 140 K were observed in flames with additional Ar and CO2 dilution, whereas temperature increases by 80 K were observed in mixtures diluted with only N2 . The microwave energy deposition to excited states begins to thermalize over scales of 100 μs, however, equilibrium is not reached before excited combustion products convect out of the probe volume on the order of several 1 ms. Understanding the impact of varying bath gases on microwave interaction, magnitude of temperature rise and thermalization timescales is critical for the development and validation of new kinetic models for applications exhibiting significant degrees of thermal non-equilibrium, such as high-speed reentry flows and plasma-assisted combustion.
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- Award ID(s):
- 1839551
- PAR ID:
- 10517945
- Publisher / Repository:
- American Institute of Aeronautics and Astronautics
- Date Published:
- Journal Name:
- AIAA SCITECH 2023 Forum
- Format(s):
- Medium: X
- Location:
- National Harbor, MD & Online
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.2514/6.2023-0166
