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Isolated n-heptane droplet combustion in microgravity: “Cool Flames” – Two-stage combustion

Published on Feb 1, 2014in Combustion and Flame4.12
· DOI :10.1016/j.combustflame.2013.09.011
Tanvir Farouk17
Estimated H-index: 17
(USC: University of South Carolina),
Frederick L. Dryer66
Estimated H-index: 66
(Princeton University)
Abstract
Abstract Recent experimentally observed two stage combustion of n -heptane droplets in microgravity is numerically studied. The simulations are conducted with detailed chemistry and transport in order to obtain insight into the features controlling the low temperature second stage burn. Predictions show that the second stage combustion occurs as a result of chemical kinetics associated with classical premixed “ Cool Flame ” phenomena. In contrast to the kinetic interactions responsible for premixed cool flame properties, those important to cool flame droplet burning are characteristically associated with the temperature range between the turnover temperature and the hot ignition. Initiation of and continuing second stage combustion involves a dynamic balance of heat generation from diffusively controlled chemical reaction and heat loss from radiation and diffusion. Within the noted temperature range, increasing reaction temperature leads to decreased chemical reaction rate and vice versa. As a result, changes of heat loss rate are dynamically balanced by heat release from chemical reaction rate as the droplet continues to burn and regress in size. At reaction temperatures below the turnover, heat loss over takes the heat release rate and extinction occurs. Should heat release exceed heat loss as the temperature increases to that for hot ignition, initiation of a high temperature burning phase may be possible. Parametric study on factors leading to initiation of the second stage burning phenomena are studied. Results show that both carbon dioxide and helium diluents can promote initiation of low temperature burning at smaller initial drop diameters than found with nitrogen as diluent. Small amounts of carbon dioxide and helium in the ambient is sufficient to activate the phenomena. The chemical kinetics dictating the second stage combustion and extinction process is also discussed.
  • References (26)
  • Citations (55)
References26
Newest
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#2Daniel L. Dietrich (Glenn Research Center)H-Index: 13
Last.Forman A. Williams (UCSD: University of California, San Diego)H-Index: 48
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#1Ruiqin Shan (UConn: University of Connecticut)H-Index: 7
#2Chun Sang Yoo (UNIST: Ulsan National Institute of Science and Technology)H-Index: 18
Last.Tianfeng Lu (UConn: University of Connecticut)H-Index: 36
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#1Yiguang Ju (Princeton University)H-Index: 54
#2Wenting Sun (Princeton University)H-Index: 20
Last.Zheng Chen (PKU: Peking University)H-Index: 30
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#1Wenting Sun (Princeton University)H-Index: 20
#2Zheng Chen (PKU: Peking University)H-Index: 30
Last.Yiguang Ju (Princeton University)H-Index: 54
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#1Marcos Chaos (Princeton University)H-Index: 22
#2Andrei F. Kazakov (Princeton University)H-Index: 24
Last.Frederick L. Dryer (Princeton University)H-Index: 66
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#1V. V. Tyurenkova (RAS: Russian Academy of Sciences)H-Index: 8
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