Journal or Book Title
Combustion and Flame
Energy transfer in a pulsed-microwave enhanced flame is investigated using hybrid fs/ps coherent anti-Stokes Raman scattering (CARS) to monitor both vibrational and rotational temperatures of nitrogen in an atmospheric pressure laminar premixed natural gas/air stagnation flame. Temperatures were measured throughout the laminar flame structure following a 30-kW peak power, 2 s duration, 3 GHz microwave pulse in a resonant waveguide cavity. CARS measurements show a delayed increase in vibrational temperature, indicating energy loading via electron impact and subsequent energy cascade. Vibrational energy thermalization was observed over timescales faster than transport through the flame zone, but slower than predicted by known vibrational-translational rates, suggesting a long-lived pathway for increased vibrational temperature. Peak vibrational temperature increases of 100 K were observed and thermalize over 100s of microseconds, resulting in a measurable increase in the rotational temperature over the same time interval. The magnitude of vibrational excitation and rate of thermalization in such plasma-assisted combustion environments is critical for applications including combustion ignition and control, and hybrid fs/ps CARS measurements provide the necessary detail on vibrational-translational relaxation processes of ground state nitrogen.
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This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.
The Combustion Institute
Dedic, Chloe E. and Michael, James B., "Thermalization dynamics in a pulsed microwave plasma-enhanced laminar flame" (2021). Mechanical Engineering Publications. 469.
Available for download on Sunday, January 22, 2023