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  • 1
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    Combustion of solid fuel in very low speed oxygen streams (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: In reduced gravity, the combustion of solid fuel in low-speed flow can be studied. The flame behavior in this low-speed regime will fill a void in our understanding of the flow effect on combustion. In addition, it is important for spacecraft fire safety considerations. In this work, modeling and experimental work on low-speed forced-concurrent-flow flame spread are carried out. In addition, experiments on reduced-gravity buoyant-flow flame spread are performed.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: The Second International Microgravity Combustion Workshop; p 245-250
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  • 2
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    Flame spread over solid fuel in low-speed concurrent flow (1995)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: This research program is concerned with the effect of low speed flow on the spreading and extinction processes of flames over solid fuels. Primary attention is given to flame propagation in concurrent flow - the more hazardous situation from the point of view of fire safety.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: The 3rd International Microgravity Combustion Workshop; p 219-225
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  • 3
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    Catalytic ignition model in a monolithic reactor with in-depth reaction (1990)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Two transient models have been developed to study the catalytic ignition in a monolithic catalytic reactor. The special feature in these models is the inclusion of thermal and species structures in the porous catalytic layer. There are many time scales involved in the catalytic ignition problem, and these two models are developed with different time scales. In the full transient model, the equations are non-dimensionalized by the shortest time scale (mass diffusion across the catalytic layer). It is therefore accurate but is computationally costly. In the energy-integral model, only the slowest process (solid heat-up) is taken as nonsteady. It is approximate but computationally efficient. In the computations performed, the catalyst is platinum and the reactants are rich mixtures of hydrogen and oxygen. One-step global chemical reaction rates are used for both gas-phase homogeneous reaction and catalytic heterogeneous reaction. The computed results reveal the transient ignition processes in detail, including the structure variation with time in the reactive catalytic layer. An ignition map using reactor length and catalyst loading is constructed. The comparison of computed results between the two transient models verifies the applicability of the energy-integral model when the time is greater than the second largest time scale of the system. It also suggests that a proper combined use of the two models can catch all the transient phenomena while minimizing the computational cost.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: NASA-CR-187791 , NAS 1.26:187791 , EMAE/TR-90-200
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  • 4
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    Catalytic ignition model in monolithic reactor with in-depth reaction (1992)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A transient model has been developed to study ignition in a monolithic catalytic reactor. Special features are the inclusion of thermal and species structures in the porous catalytic layer and the resolution of small-time-scale events. Catalyst loading is used as a parameter to study these structure variations before and after ignition. Regions where the catalytic reaction is kinetically controlled and regions where the reaction is diffusionally controlled are identified in both steady and transient states.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: In: Aerothermodynamics in combustors; IUTAM Symposium, National Taiwan Univ., Taipei, June 3-5, 1991, Selected Papers (A93-51626 22-25); p. 231-244.
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  • 5
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    Modelling ignition characteristics of rich H2/O2 mixture in a monolithic catalytic reactor (1988)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Ignition of rich hydrogen-oxygen mixture in a monolithic catalytic reactor is studied using a transient combustion model. The model assumes a quasi-steady gas phase and a thermally-thin substrate. The ignition time lag is due to the thermal inertia of the substrate. One-step global chemical reaction is assumed both on the surface and in the gas phase. An effectiveness factor is introduced to account for the transition from a kinetically-limited catalytic surface reaction to a diffusion-limit one during ignition. Results presented include a catalytic ignition boundary, ignition delay time and the transient response in the catalytic bed.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: AIAA PAPER 88-3224
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  • 6
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    Size and shape of solid fuel diffusion flames in very slow speed flows (1987)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The influence of very low speed forced flows on the size and shape of a diffusion flame adjacent to a solid fuel slab is studied experimentally and theoretically. Velocities in the range of 1.5 to 6.3 cm/s and O2 mole fractions (in the O2/N2 atmosphere) in the range of 0.15 to 0.19 were tested. The flames moved farther from the fuel surface as the flow velocity was reduced and closer to the sample as the O2 concentration was lowered. A corresponding theoretical model was solved using a two-dimensional Navier-Stokes system with a one-step finite-rate chemical reaction and surface radiative loss.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: AIAA PAPER 87-2030
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  • 7
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    Downward Diffusion Flame Spread and Extinction in Variable Gravitational Fields - Lunar and Martian Simulations (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: This paper describes experimental observations of downward, opposed-flow flame spreading made under partial-gravity conditions aboard NASA research aircraft. Flame spreading and flammability limit behavior of a thin cellulosic fuel tested at normal pressure in oxygen/nitrogen mixtures of 21 percent oxygen, by volume, and below are described over effective acceleration levels ranging from 0.05 to 0.6 times normal earth gravity. Downward burning flammability and flame spread rates are shown to be enhanced by reductions in gravitational acceleration. These data have fire safety implications for the planning of lunar and Martian outposts.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: AIAA PAPER 93-0828 , E-8377 , ; 8 p.|AIAA, Aerospace Sciences Meeting and Exhibit; Jan 11, 1993 - Jan 14, 1993; Reno, NV; United States
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  • 8
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    Numerical Computation of Low-Speed Concurrent Flow Flame Spread in Mixed Buoyant and Forced Flow (1993)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The effect of low-speed mixed convection (forced plus buoyant) on concurrent flow flame spread over a thin solid is examined. Computations are carried out using an existing model. Results indicate that seemingly small levels of gravity can significantly alter flame spread rates. Starting with a purely forced flow condition, as gravity is added, the entrainment due to buoyancy lengthens the flame and increases the spread rate significantly. Buoyancy has an influence on the extinction limits. At low speed, the presence of a small gravity level widens the flammability limit.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: AIAA PAPER 93-0827 , E-8360 , AIAA, Aerospace Sciences Meeting and Exhibit; Jan 11, 1993 - Jan 14, 1993; Reno, NV; United States|; 8 p.
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  • 9
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    The possibility of a reversal of material flammability ranking from normal gravity to microgravity (1990)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The purpose of the discussion is to show, by a theoretical model, that one of the material flammability indices, the flammability limit, can be reversed in proper circumstances. A stagnation-point diffusion flame adjacent to a spherical solid-fuel surface is considered. It is shown that a reversal of the limiting oxygen indices from normal gravity and microgravity is possible. Although the example is based on a particular theoretical model with a particular flame configuration and specifically for an oxygen limit, the flammability-limit reversal phenomenon is believed to be more general.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: Combustion and Flame (ISSN 0010-2180); 80; 355-357
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  • 10
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    Near-Limit Flame Spread over a Thin Solid Fuel in Microgravity (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Diffusion flame spread over a thin solid fuel in quiescent and slowly moving atmospheres is studied in microgravity. The flame behavior is observed to depend strongly on the magnitude of the relative velocity between the flame and the atmosphere. In particular, a low velocity quenching limit is found to exist in low oxgen environments. Using both the microgravity results and previously published data at high opposed-flow velocities, the flame spread behavior is examined over a wide velocity range. A flammability map using molar oxygen percentages and characteristic relative velocities as coordinates is constructed. Trends of flame spread rate are determined and mechanisms for flame extinction are discussed.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: E-8357 , Symposium (International) on Combustion; Aug 14, 1988 - Aug 19, 1988; Seattle, WA; United States
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