Doctoral Dissertations

Date of Award

5-1996

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Physics

Major Professor

Christian Parigger

Committee Members

Lloyd M. Davis

Abstract

Laser-induced breakdown is studied in ammonia and ammonia-oxygen gaseous mixtures. We investigate the emission spectra of the NH and N2 diatomic molecules in pure ammonia optical plasmas using multispecies spontaneous emission spectroscopy. Gas temperatures are inferred in the decaying optical plasma by theoretical repro-ductions of the experimental spectra. Laser-induced breakdown microplasmas (laser sparks) are used to ignite combustible ammonia-oxygen gaseous mixtures. We de-termine the minimum ignition energy requirements and laminar flame speeds over much of the flammability limits of these gas mixtures. The experimentally deter-mined flame speeds are compared to theoretical laminar flame speeds. High-speed shadowgraph photography and planar laser-induced fluorescence imaging of the NH free radical is used to study the temporal and spatial development of the optical plasma in combustible and noncombustible ammonia-oxygen mixtures. Knowledge of the spatial and temporal evolution of gas temperature and species concentrations as well as spatial symmetries in the laser-induced breakdown plasma is essential for numerical modeling of laser-spark ignition. Experimentally determined quantities such as temperature, free-radical relative number densities, minimum ig-nition energies, and flame speeds can be used to validate such models. In all laser-induced breakdown studies, the optical discharge was created by fo-cusing Q-switched Nd:YAG laser 1.064 micrometer wavelength pulses into the gas sample. Focused laser-pulse intensities range from lO's to IDG's of GW/cm2.

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