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  • 11
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    Effects of particulate radiation on premixed gas flames (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Observations of the effect of the addition of fine solid particles to weakly combustible methane-air mixtures are reported. Burning rates, pressure rise, and thermal characteristics are found to exhibit nonmonotonic trends with increasing particle loading. These results are interpreted in terms of the effects of augmentation of radiant loss at small particle loadings and re-absorption of emitted radiation at larger loadings. It is suggested that in sufficiently large systems, flammability limits might not exist because of this reabsorption effect.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: AIAA PAPER 93-0711 , AIAA, Aerospace Sciences Meeting and Exhibit; Jan 11, 1993 - Jan 14, 1993; Reno, NV; United States|; 7 p.
    Format: text
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    NASA TECHNICAL REPORTS
  • 12
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    Effects of Radiative and Diffusive Transport Processes on Premixed Flames near Flammability Limits (1991)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: A study of the mechanisms of flammability limits and the dynamics of flame extinguishment in premixed gas flames is described, a novel feature of which is the use of diluent gases having a wide range of radiative and diffusive transport properties. This feature enables an assessment of the importance of volumetric heat losses and Lewis number effects on these mechanisms. Additionally, effects of flame dynamics and flame front curvature are studied by employing spherically expanding flames obtained in a microgravity environment whereby natural convection is eliminated. New diagnostics include chamber pressure measurements and the first reported species concentration measurements in a microgravity combustion experiment. The limit mechanisms and extinguishment phenomena are found to be strongly influenced by the combined effects of radiant heat loss, Lewis number and flame curvature. Two new and as yet not well understood phenomena are reported: 'double flames' in rich H2-O2-CO2 mixtures and an 'inverse flammability region' in rich C3H8-O2-CO2 mixtures.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: E-8364 , International Symposium on Combustion; Jul 22, 1990 - Jul 27, 1990; Orleans; France
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  • 13
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    Studies of premixed laminar and turbulent flames at microgravity (1993)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A two and one-half year experimental and theoretical research program on the properties of laminar and turbulent premixed gas flames at microgravity was conducted. Progress during this program is identified and avenues for future studies are discussed.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: NASA-CR-194656 , NAS 1.26:194656
    Format: application/pdf
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  • 14
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    Studies of Radiation-Driven and Buoyancy-Driven Fluid Flows and Transport (1994)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: It is well known that radiative heat transport influences many types of buoyant flows due to its effect on the temperature and thus density field in the fluid medium. It is of interest to study gaseous flows driven solely by radiation in the absence of buoyancy, particularly because of its application to astrophysical flows that are well known from astronomical observations and numerical simulation. However, no laboratory-scale experiments of this phenomenon have ever been conducted. To study the possibility of obtaining such flows in the laboratory, an apparatus was built to produce large temperature differences (Delta T) up to 300 K in a gas confined between flat parallel plates. SF6 was used as the radiatively-active gas because its Planck absorption length is much shorter than that of any other common non-reactive gas. The NASA-Lewis 2.2 second drop tower was used to obtain reduced gravity in order to suppress buoyancy effects. To image the resulting flows, a laser shearing interferometer was employed. Initial results indicate the presence of flow that does not appear to be attributable to the residual flow resulting from buoyancy influences before the drop. For Delta T greater than 70 K, slight deformations in the interferometer fringes seen at lower Delta T became large unsteady swirls. Such behavior did not occur for radiatively-inactive gases, suggesting that a flow driven solely by radiation was obtained in SF6 and to a lesser extent in CO2 This was more pronounced at higher pressures and plate spacings, consistent with our scaling predictions.
    Keywords: Fluid Mechanics and Heat Transfer
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  • 15
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    Self-organized Spiral and Circular Waves in Premixed Gas Flames (1994)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A diffusive-thermal high Lewis number (Le) gas-phase oscillator has been observed in premixed flames using a lean mixture of butane and oxygen diluted with helium (Le approx. 3.0). This reactive-diffusive system exhibits both propagating radial pulsations and rotating spiral waves perhaps,analogous to those observed in other excitable media such as the Belousov-Zhabotinsky reaction.
    Keywords: Inorganic and Physical Chemistry
    Type: NASA-TM-111761 , NAS 1.15:111761 , E-9553 , Journal of Chemical Physics (ISSN 0021-9606); 101; 3; 2632-2633
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