Synthetic gas, syngas, is a popular alternative fuel for the gas turbine industry, but the composition of syngas can contain different types and amounts of contaminants, such as carbon dioxide, methane, moisture, and nitrogen, depending on the industrial process involved in its manufacturing. The presence of steam in syngas blends is of particular interest from a thermo-chemical perspective as there is limited information available in the literature. This study investigates the effect of moisture content (0 ? 15% by volume), temperature (323 ? 423 K), and pressure (1 ? 10 atm) on syngas mixtures by measuring the laminar flame speed in a newly developed constant-volume, heated experimental facility. This heated vessel also broadens the experimental field of study in the authors? laboratory to low vapor pressure fuels and other vaporized liquids. The new facility is capable of performing flame speed experiments at an initial pressure as high as 30 atm and an initial temperature up to 600 K. Several validation experiments were performed to demonstrate the complete functionality of the flame speed facility. Additionally, a design-of-experiments methodology was used to study the mentioned syngas conditions that are relevant to the gas turbine industry. The design-of-experiments methodology provided the capability to identify the most influential factor on the laminar flame speed of the conditions studied. The experimental flame speed data are compared to the most up-to-date C4 mechanism developed through collaboration between Texas A&M and the National University of Ireland Galway. Along with good model agreement shown with all presented data, a rigorous uncertainty analysis of the flame speed has been performed showing an extensive range of values from 4.0 cm/s to 16.7 cm/s. The amount of carbon monoxide dilution in the fuel was shown to be the most influential factor on the laminar flame speed from fuel lean to fuel rich. This is verified by comparing the laminar flame speed of the atmospheric mixtures. Also, the measured Markstein lengths of the atmospheric mixtures are compared and do not demonstrate a strong impact from any one factor but the ratio of hydrogen and carbon monoxide plays a key role. Mixtures with high levels of CO appear to stabilize the flame structure of thermal-diffusive instability. The increase of steam dilution has only a small effect on the laminar flame speed of high-CO mixtures, while more hydrogen-dominated mixtures demonstrate a much larger and negative effect of increasing water content on the laminar flame speed.

Thesis (Ph. D.)--University of Chicago, Dept. of Physics, 2001. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.

Thesis (M. Phil.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves 59-61).

In this thesis, We will focus on discussing the Andreev tunneling and Josephson tunneling of underdoped cuprate superconductors. In particular, we emphasize how the pseudogap of the underdoped cuprate influences these tunneling behaviors. Our calculation is based on the theory of YRZ Green’s function in which the pseudogap acts as a precursor to the undoped Mott insulator. In the study of Andreev tunneling, the tunneling spectroscopy we obtained exhibits a two-gap feature, i. e., a small energy gap associated with Andreev reflection in the transparent limit and a large gap associated with single particle tunneling. Our results are in good agreement with the two-gap scenario observed in tunneling experiments for underdoped cuprate. In the study of Josephson tunneling, we aimed to test the proposal of “cooperon physics” by examining the Josephson coupling between two optimally doped (or overdoped) cuprate superconductors separated by a barrier of an underdoped-cuprate in its pseudogap state with finiteenergy cooperon excitation. Our calculation shows a significant contribution from the cooperon excitation to the Josephson coupling, which is comparable to that from nodal quasiparticles. Moreover, our results give a good description of the temperature-dependent enhanced Josephson tunneling revealed in experiments. / published_or_final_version / Physics / Doctoral / Doctor of Philosophy

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