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Laser Diagnostics of Reacting Molecular Plasmas for Plasma Assisted Combustion Applications

Winters, Caroline

Abstract Details

2017, Doctor of Philosophy, Ohio State University, Aero/Astro Engineering.
This work has produced extensive sets of new data on low-temperature plasma-assisted fuel oxidation in hydrogen-oxygen-argon and hydrocarbon-oxygen-argon mixtures. The measurements have been made in two different plasma flow reactors, at an initial temperature of 500 K and pressures ranging from 300 Torr to 700 Torr. In both reactors, the plasma is generated by a high peak voltage, ns pulse discharge, operated at high pulse repetition rates (up to 20 kHz). Metastable Ar atom number density distributions in the discharge afterglow are measured by Tunable Diode Laser Absorption Spectroscopy (TDLAS), and used to characterize plasma uniformity. Temperature in the discharge-excited reacting flow is measured by Rayleigh scattering. Two-photon Absorption Laser Induced Fluorescence (TALIF) is used to measured absolute H and O atom number densities. The results are compared with predictions of a kinetic model analyzing reaction kinetics of excited species and radicals generated by the plasma at low temperatures and high pressures. The modeling predictions show good agreement with the data, with the exception of fuel-limited mixtures, when nearly all fuel available in the mixture of reactants is oxidized in the discharge. Kinetic modeling analysis identified dominant processes of generation and decay of atomic and radical species in the discharge and in the afterglow. At the present low-temperature conditions, the effect of chain branching reactions on plasma-assisted fuel oxidation kinetics is insignificant. In addition, this work presents results of time-resolved, absolute measurements of OH number density by Laser Induced Fluorescence (LIF), as well as measurements of translations-rotational temperature and nitrogen vibrational temperature by ns broadband Coherent Anti-Stokes Raman Scattering (CARS), in air and lean hydrogen-air mixtures excited in a diffuse filament ns pulse discharge at high specific energy loading. The main objective of these measurements is to study kinetics of OH radicals at the conditions of strong vibrational excitation of nitrogen, below autoignition temperature. The results show that OH number density and N2 vibrational temperature exhibit transient maxima after the discharge pulse. Comparison of the experimental data with kinetic modeling predictions shows that OH kinetics is controlled primarily by reactions of H2 and O2 with O and H atom generated during the discharge. At the present conditions, OH number density is not affected by N2 vibrational excitation directly, e.g. vibrational energy transfer to HO2. However, as the energy is increased, the model also predicts transient OH number density overshoot, due to the temperature rise caused by N2 vibrational relaxation by O atoms. This may well be the dominant effect on OH number density in discharges with high specific energy loading. Finally, the present work provides insight into surface charge dynamics and kinetics of radical species reactions in nanosecond pulse discharges sustained at a liquid-vapor interface, above a distilled water surface. LIF and TALIF line imaging are used for in situ measurements of spatial distributions of absolute OH and H atom number densities in near-surface, repetitive nanosecond pulse discharge plasmas.
Igor Adamovich, Dr. (Advisor)
Jeffrey Sutton, Dr. (Committee Member)
Seung Hyun Kim, Dr. (Committee Member)
228 p.

Recommended Citations

Citations

  • Winters, C. (2017). Laser Diagnostics of Reacting Molecular Plasmas for Plasma Assisted Combustion Applications [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1503306596261748

    APA Style (7th edition)

  • Winters, Caroline. Laser Diagnostics of Reacting Molecular Plasmas for Plasma Assisted Combustion Applications. 2017. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1503306596261748.

    MLA Style (8th edition)

  • Winters, Caroline. "Laser Diagnostics of Reacting Molecular Plasmas for Plasma Assisted Combustion Applications." Doctoral dissertation, Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1503306596261748

    Chicago Manual of Style (17th edition)