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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

SPATIOTEMPORALLY RESOLVED MID-INFRAREDEMISSION AND ABSORPTION SPECTROSCOPYDIAGNOSTICS FOR PROPELLANT FLAMES

Austin J McDonald (18423771) 24 April 2024 (has links)
<p dir="ltr">Emission and absorption spectroscopy diagnostics are useful for providing non-invasive,<br>quantitative measurements of various gas properties in combustion environments, including<br>temperature and species concentrations. These measurements become even more useful<br>when they are applied with high spatial and temporal resolution. This dissertation describes<br>several ways that both emission and absorption diagnostics were advanced through leveraging<br>improvements in mid-IR camera and laser technology and through refining the use of existing<br>techniques.<br>A literature review is provided for both laser absorption and emission spectroscopy. Previous advancements in spatially resolved techniques are explained. The fundamental equations<br>of spectroscopic diagnostics are reviewed, starting from statistical mechanics.<br>A spectrally-resolved emission imaging diagnostic is presented. This diagnostic provided<br>1-dimensional measurements of gas temperature and relative mole fraction of CO<sub>2</sub> and HCl<br>in flames. An imaging spectrometer and a high-speed mid-infrared camera were used to<br>provide 1D measurements of CO<sub>2</sub><sub> </sub>and HCl emission spectra with a spectral resolution of<br>0.46 cm<sup>-1</sup> at rates up to 2 kHz. Measurements were acquired in HMX and AP-HTPB flames<br>burning in air at 1 atm. This diagnostic was applied to characterize how the path-integrated<br>gas temperature of HMX flames varies in time and with distance above the burning surface.<br>Additionally, Abel inversion with Tikhonov regularization was applied to determine the radial<br>distribution of temperature and relative concentration of CO<sub>2</sub> and HCl within the core of<br>AP-HTPB flames.<br>Next, a similar emission imaging diagnostic is presented which uses spectrally-resolved<br>measurements of emission spectra at visible wavelengths, unlike the mid-infrared measure-<br>ments in the rest of this dissertation. This diagnostic provided 1D temperature measure-<br>ments of aluminum oxide (AlO), an intermediate product of aluminum combustion. While<br>this author created the AlO diagnostic, these measurements were performed alongside a CO<br>absorption diagnostic used by a different researcher to compare the flame bath gas (via CO)<br>and the region immediately around aluminum particles (via AlO) when varying forms of<br>aluminum powder were used in a propellant. This comparison allows analysis of the burning regime of aluminum particles. Evidence was found that nano-aluminum particles burn in<br>the kinetically controlled combustion regime, while micron-aluminum particles burn in the<br>diffusion-controlled regime.<br>Multi-spectral emission imaging of hypergolic ignition of ammonia borane (AB) is then<br>presented. Three high-speed cameras with multiple optical filters were used to capture<br>infrared and visible wavelength videos of four individual species during AB ignition: BO,<br>BO<sub>2</sub>, HBO<sub>2</sub>, and the B-H stretch mode of AB were imaged. The ignition process was<br>observed to act in two steps: gas evolution and then propagation of a premixed flame. The<br>evolution of the species and flame front revealed that boranes may continue to complete<br>combustion to a further degree than other boron fuels. This author performed the infrared<br>camera imaging and also ran infrared spectrograph measurements to confirm which species<br>were viewed through the optical filters.<br>Next, a scanned-wavelength direct-absorption diagnostic for directly measuring NH<sub>3</sub> in<br>high-temperature combustion environments is presented. A quantum cascade laser (QCL)<br>was scanned at 5 kHz over multiple NH<sub>3</sub> transitions between 959.9 cm<sup>−</sup><sup>1</sup> and 960.3 cm<sup>−</sup><sup>1</sup> to<br>measure path-integrated NH<sub>3</sub> temperature and mole fraction. Many NH<sub>3</sub> transitions overlap<br>with high-temperature water lines at commonly used diagnostic frequencies, severely limiting<br>those diagnostics’ capabilities in water-rich, high-temperature environments that are typical<br>of combustion applications. The optical frequencies used in this diagnostic are insensitive<br>to water absorption and thus remedy this issue. This diagnostic was demonstrated within<br>the flame of ammonia borane. AB-based fuels were burned in ambient air and translated<br>vertically to effectively scan the measurement line-of-sight vertically through the flame. Ad-<br>ditionally, flames of these fuels were characterized at a stationary height in an opposed-flow<br>burner (OFB) under O<sub>2</sub> flow.<br>The final chapter presents scanned-wavelength direct-absorption measurements of path-<br>integrated temperature and CO mole fraction in opposed-flow diffusion flames of hydroxyl-<br>terminated polybutadiene (HTPB). HTPB strands were held in an opposed-flow burner<br>under an opposed flow of O2 or 50/50 O<sub>2</sub>/N<sub>2</sub> to create quasi-steady and quasi-1D diffusion<br>flames above the fuel strand. The opposed-flow burner was translated vertically to effectively<br>scan the measurement line-of-sight vertically through the flame. A quantum-cascade laser (QCL) was scanned across the P(2,20), P(0,31), and P(3,14) absorption transitions in CO’s<br>fundamental vibration bands near 2008 cm<sup>−</sup><sup>1</sup> at 10 kHz to determine the path-integrated<br>temperature and CO mole fraction. The laser beam was passed through sapphire rods<br>held close to the flame edge to bypass the flame boundary and provide a well defined path<br>length for mole fraction measurements. The measured profiles and fuel regression rates<br>were compared to predictions produced by a steady opposed-flow 1D diffusion flame model<br>produced by researchers at the Army Research Lab. The model was generated with chemical<br>kinetics mechanisms employing two different assumptions for the nascent gaseous product of<br>HTPB pyrolysis: C<sub>4</sub>H<sub>6</sub> or C<sub>20</sub>H<sub>32</sub>. It was found that the C<sub>20</sub>H<sub>32</sub> model produced temperature<br>and CO profiles along with regression rates that agreed more closely with the measured<br>results.<br></p>

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