Lifted flame speed enhancement by plasma excitation of oxygen

Timothy Ombrello, Sang Hee Won, Yiguang Ju, Skip Williams

Research output: Chapter in Book/Report/Conference proceedingConference contribution

6 Scopus citations

Abstract

Oxygen containing plasmas produce several species that have a greater oxidation potential than molecular oxygen in its 3Σ ground state. These species include O, O3 and O2 in metastable excited states, namely 1Δ and 1Σ. In experiments that explore the enhancement of combustion processes with plasma, it has been difficult to isolate the various enhancement mechanisms. In this study, two oxygen containing plasma-produced species, O3 and O 2(a1Δg), have been produced successfully in a microwave plasma, isolated in the afterglow, quantified and transported to C3H8 and C2H4 lifted flames. Significant kinetic enhancement by O3 and O2(a 1Δg) were observed for each flame by comparing flame stabilization locations with and without the plasma generated species. Atmospheric pressures were utilized to investigate the effects of O3 and showed up to a 10% enhancement in the flame speed for 1300 ppm of O 3 addition to the O2/N2 oxidizer of lifted C3H8 flames. Numerical simulations showed that the O 3 decomposition early in the preheat zone of the flame produced O which rapidly reacted with C3H8 to abstract an H, which led to OH production. The subsequent reaction of the OH with fuel fragments produced H2O and other stable species, yielding chemical heat release to enhance the flame speed. The effect of O2(a1Δ g) was studied at low pressure (27 Torr) and was isolated by adding NO to the plasma afterglow to eliminate O3. For transport times on the order of one second in the presence of NO, the only remaining oxygen species were O2(X3Δg) and O2(a 1Δg). Under these conditions, the enhancement of O2(a1Δg) could be studied in isolation, becoming an ideal source for combustion experiments. It was found that O 2(a1Δg) was a better oxidizer than O 2 by significantly enhancing the propagation speed of C2H4 flames. The present experimental results will have a direct impact on the development of elementary reaction rates with O2(a1Δg) and O3 at flame conditions to establish detailed plasma-flame kinetic mechanisms.

Original languageEnglish (US)
Title of host publication47th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition
PublisherAmerican Institute of Aeronautics and Astronautics Inc.
ISBN (Print)9781563479694
DOIs
StatePublished - 2009

Publication series

Name47th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition

All Science Journal Classification (ASJC) codes

  • Space and Planetary Science
  • Aerospace Engineering

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    Ombrello, T., Won, S. H., Ju, Y., & Williams, S. (2009). Lifted flame speed enhancement by plasma excitation of oxygen. In 47th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition [2009-0689] (47th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition). American Institute of Aeronautics and Astronautics Inc.. https://doi.org/10.2514/6.2009-689