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Cool-flame Extinction During N-Alkane Droplet Combustion in MicrogravityRecent droplet combustion experiments onboard the International Space Station (ISS) have revealed that large n-alkane droplets can continue to burn quasi-steadily following radiative extinction in a low-temperature regime, characterized by negative-temperaturecoefficient (NTC) chemistry. In this study we report experimental observations of n-heptane, n-octane, and n-decane droplets of varying initial sizes burning in oxygen/nitrogen/carbon dioxide and oxygen/helium/nitrogen environments at 1.0, 0.7, and 0.5 atmospheric pressures. The oxygen concentration in these tests varied in the range of 14% to 25% by volume. Large n-alkane droplets exhibited quasi-steady low-temperature burning and extinction following radiative extinction of the visible flame while smaller droplets burned to completion or disruptively extinguished. A vapor-cloud formed in most cases slightly prior to or following the "cool flame" extinction. Results for droplet burning rates in both the hot-flame and cool-flame regimes as well as droplet extinction diameters at the end of each stage are presented. Time histories of radiant emission from the droplet captured using broadband radiometers are also presented. Remarkably the "cool flame" extinction diameters for all the three n-alkanes follow a trend reminiscent of the ignition delay times observed in previous studies. The similarities and differences among the n-alkanes during "cool flame" combustion are discussed using simplified theoretical models of the phenomenon
Document ID
20140006750
Document Type
Conference Paper
Authors
Nayagam, Vedha (Case Western Reserve Univ. Cleveland, OH, United States)
Dietrich, Daniel L. (NASA Glenn Research Center Cleveland, OH United States)
Hicks, Michael C. (NASA Glenn Research Center Cleveland, OH United States)
Williams, Forman A. (California Univ., San Diego La Jolla, CA, United States)
Date Acquired
June 4, 2014
Publication Date
March 15, 2014
Subject Category
Inorganic, Organic and Physical Chemistry
Report/Patent Number
GRC-E-DAA-TN13650
Meeting Information
2014 Spring Technical Meeting of the Central States Section of the Combustion Institute(Tulsa, OK)
Funding Number(s)
WBS: WBS 904211.04.02.30.07
CONTRACT_GRANT: NNC13BA101
Distribution Limits
Public
Copyright
Public Use Permitted.
Keywords
microgravity combustion
Droplet combustion
methanol

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