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Droplet Combustion Experiments Aboard the International Space Station

Published on Oct 1, 2014in Microgravity Science and Technology1.97
· DOI :10.1007/s12217-014-9372-2
Daniel L. Dietrich13
Estimated H-index: 13
(Glenn Research Center),
Vedha Nayagam4
Estimated H-index: 4
(Case Western Reserve University)
+ 9 AuthorsForman A. Williams48
Estimated H-index: 48
(UCSD: University of California, San Diego)
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Abstract
This paper summarizes the first results from isolated droplet combustion experiments performed on the International Space Station (ISS). The long durations of microgravity provided in the ISS enable the measurement of droplet and flame histories over an unprecedented range of conditions. The first experiments were with heptane and methanol as fuels, initial droplet droplet diameters between 1.5 and 5.0 m m, ambient oxygen mole fractions between 0.1 and 0.4, ambient pressures between 0.7 and 3.0 a t m and ambient environments containing oxygen and nitrogen diluted with both carbon dioxide and helium. The experiments show both radiative and diffusive extinction. For both fuels, the flames exhibited pre-extinction flame oscillations during radiative extinction with a frequency of approximately 1 H z. The results revealed that as the ambient oxygen mole fraction was reduced, the diffusive-extinction droplet diameter increased and the radiative-extinction droplet diameter decreased. In between these two limiting extinction conditions, quasi-steady combustion was observed. Another important measurement that is related to spacecraft fire safety is the limiting oxygen index (LOI), the oxygen concentration below which quasi-steady combustion cannot be supported. This is also the ambient oxygen mole fraction for which the radiative and diffusive extinction diameters become equal. For oxygen/nitrogen mixtures, the LOI is 0.12 and 0.15 for methanol and heptane, respectively. The LOI increases to approximately 0.14 (0.14 O 2/0.56 N 2/0.30 C O 2) and 0.17 (0.17 O 2/0.63 N 2/0.20 C O 2) for methanol and heptane, respectively, for ambient environments that simulated dispersing an inert-gas suppressant (carbon dioxide) into a nominally air (1.0 a t m) ambient environment. The LOI is approximately 0.14 and 0.15 for methanol and heptane, respectively, when helium is dispersed into air at 1 atm. The experiments also showed unique burning behavior for large heptane droplets. After the visible hot flame radiatively extinguished around a large heptane droplet, the droplet continued to burn with a cool flame. This phenomena was observed repeatably over a wide range of ambient conditions. These cool flames were invisible to the experiment imaging system but their behavior was inferred by the sustained quasi-steady burning after visible flame extinction. Verification of this new burning regime was established by both theoretical and numerical analysis of the experimental results. These innovative experiments have provided a wealth of new data for improving the understanding of droplet combustion and related aspects of fire safety, as well as offering important measurements that can be used to test sophisticated evolving computational models and theories of droplet combustion.
  • References (27)
  • Citations (30)
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References27
Newest
#1Vedha NayagamH-Index: 13
#2Daniel L. Dietrich (Glenn Research Center)H-Index: 13
Last.Forman A. Williams (UCSD: University of California, San Diego)H-Index: 48
view all 5 authors...
#1Christopher Dembia (Cornell University)H-Index: 6
#2Yu Cheng Liu (Cornell University)H-Index: 10
Last.C. Thomas Avedisian (Cornell University)H-Index: 14
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#1Yiguang Ju (Princeton University)H-Index: 54
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#1V. V. Tyurenkova (RAS: Russian Academy of Sciences)H-Index: 8
#2V.V. Tyurenkova (RAS: Russian Academy of Sciences)
#1Forman A. Williams (UCSD: University of California, San Diego)H-Index: 48
#2Vedha Nayagam (Case Western Reserve University)H-Index: 13
Last.Vedha Nayagam (Case Western Reserve University)H-Index: 4
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#1Masato Mikami (Yamaguchi University)H-Index: 14
#2Yasuko Yoshida (Yamaguchi University)H-Index: 1
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#1Fahd E. Alam (USC: University of South Carolina)H-Index: 4
#2Ali Charchi Aghdam (USC: University of South Carolina)
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#1Tanvir Farouk (USC: University of South Carolina)H-Index: 17
#2Daniel L. Dietrich (Glenn Research Center)H-Index: 13
Last.Frederick L. Dryer (Princeton University)H-Index: 66
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#1C. L. Vang (UC Davis: University of California, Davis)
#2B. D. Shaw (UC Davis: University of California, Davis)
#1Changxiao Shao (ZJU: Zhejiang University)H-Index: 4
#2LUOKun (ZJU: Zhejiang University)H-Index: 23
Last.Jianren Fan (ZJU: Zhejiang University)H-Index: 27
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#1Vedha Nayagam (Case Western Reserve University)H-Index: 13
#2Vedha Nayagam (Case Western Reserve University)H-Index: 4
Last.Forman A. Williams (UCSD: University of California, San Diego)H-Index: 48
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View next paperIsolated n-heptane droplet combustion in microgravity: “Cool Flames” – Two-stage combustion