| 說明 |
210 p |
| 附註 |
Source: Dissertation Abstracts International, Volume: 67-04, Section: B, page: 2185 |
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Adviser: Alessandro Gomez |
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Thesis (Ph.D.)--Yale University, 2006 |
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The present work analyzed computationally and experimentally the birth and propagation of ignition and extinction fronts. In this work, prior to the study of these unsteady phenomena, two steady cases were considered: flat counterflow diffusion flames, and standing edge flames. The former was the preliminary necessary step to the unsteady case, while the latter was a particular case of ignition front in the absence of inertial effects |
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A vorticity-velocity formulation was developed and employed in the computational modeling of all the steady and unsteady methane flames. First, the reliability of the formulation was shown by demonstrating consistency with computational results from well-validated one-dimensional counterflow codes [CLUS90] |
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Additional steps toward the validation of the computational results were the simulations of (a) a steady two-dimensional axisymmetric methane/enriched-air counterflow diffusion flame and (b) a steady two-dimensional axisymmetric methane/enriched-air counterflow edge flame. The computational results for this flame were compared with the corresponding experimental data. The model used experimental boundary conditions and was quantitatively validated with respect to measurements of the velocity field, the CO LIF signal, the OH LIF signal, and the reaction rate for CO + OH → CO2 + H. The comparison between the experimental and computational data yielded excellent agreement for all the measured quantities |
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Lastly, the model was applied to the study of unsteady partially premixed fronts. A steady flat diffusion flame was perturbed by two counter-rotating vortex rings issued both from the oxidizer side and the fuel side. Excellent agreement was observed throughout the interaction between computational and experimental results. The validated model was used to study details of the interaction with high temporal and spatial resolution |
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In the ignition mode, an edge flame typically exhibits a well-characterized structure, with the characteristic premixed "hook" of an edge flame, with a lean branch, a stoichiometric segment that evolves into the remnant of the original diffusion flame, and a much weaker secondary diffusion flame. Surprisingly, in the simulated flames, no evidence was found of a rich premixed branch in the edge flame in the ignition mode. Ignition edge flames were characterized by positive laminar flame speeds, that is, they propagated toward the unburned mixture |
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In the extinction mode, the edge flames presented a simple edge, had no rate maximum near the edge and appeared to be receding away from the unburned mixture, as essentially a two-dimensional diffusion flame. The flame exhibited a negative propagation speed several times the value of SL, the speed of a freely propagating stoichiometric premixed flame. (Abstract shortened by UMI.) |
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School code: 0265 |
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DDC |
| Host Item |
Dissertation Abstracts International 67-04B
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| 主題 |
Engineering, Mechanical
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0548
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| Alt Author |
Yale University
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