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Cool-flame Extinction During N-Alkane Droplet Combustion in Microgravity
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Author and Affiliation:
Nayagam, Vedha(Case Western Reserve Univ., Dept. of Mechanical and Aerospace Engineering, 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)
Abstract: Recent 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
Publication Date: Mar 15, 2014
Document ID:
20140006750
(Acquired Jun 26, 2014)
Subject Category: INORGANIC, ORGANIC AND PHYSICAL CHEMISTRY
Report/Patent Number: GRC-E-DAA-TN13650
Document Type: Conference Paper
Meeting Information: 2014 Spring Technical Meeting of the Central States Section of the Combustion Institute; 16-18 March 2014; Tulsa, OK; United States
Meeting Sponsor: Combustion Inst.; Pittsburgh, PA, United States
Contract/Grant/Task Num: NNC13BA101; WBS 904211.04.02.30.07
Financial Sponsor: NASA Glenn Research Center; Cleveland, OH United States
Organization Source: NASA Glenn Research Center; Cleveland, OH United States
Description: 9p; In English; Original contains color illustrations
Distribution Limits: Unclassified; Publicly available; Unlimited
Rights: Copyright; Distribution as joint owner in the copyright
NASA Terms: ALKANES; HYDROCARBON FUELS; COMBUSTION; EXTINCTION; FLAME TEMPERATURE; MICROGRAVITY; BURNING RATE; DROPS (LIQUIDS); INTERNATIONAL SPACE STATION; INTERNAL COMBUSTION ENGINES; QUASI-STEADY STATES; HEPTANES; LOW TEMPERATURE; RADIOMETERS; OXYGEN; ATMOSPHERIC PRESSURE
Other Descriptors: MICROGRAVITY COMBUSTION; METHANOL; DROPLET COMBUSTION
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