Oscillatory cool flame combustion behavior of submillimeter sized n-alkane droplet under near limit conditions

Published on Jan 1, 2019
· DOI :10.1016/j.proci.2018.05.151
Fahd E. Alam4
Estimated H-index: 4
(USC: University of South Carolina),
Ali Charchi Aghdam (USC: University of South Carolina)+ 1 AuthorsTanvir Farouk17
Estimated H-index: 17
(USC: University of South Carolina)
Abstract This paper reports simulation results of oscillatory cool flame burning of an isolated, submillimeter sized n-heptane (n-C 7 H 16 ) droplet in a selectively ozone (O 3 ) seeded nitrogen-oxygen (N 2 -O 2 ) environments at atmospheric pressure. An evolutionary one-dimensional droplet combustion code encompassing relevant physics and detailed chemistry was employed to explore the roles of low-temperature chemistry, O 3 seeding, and dynamic flame structure on burning behaviors. For X O2 = 21% and a range of selective ozone seeding, near-quasi-steady cool flame burning is achieved directly (without requiring hot flame initiation and radiative extinction). Under low oxygen index conditions, but with significant O 3 seeding (X O3 = 5%), a nearly quasi-steady cool flame is initially established that then transitions to a dynamically oscillating cool flame burning mode which continues until the droplet is completely consumed. It is found that the oscillation occurs as result of a initial depletion of fuel vapor-oxidizer layer evolving near the droplet surface and its dynamic re-establishment through liquid vaporization and vapor/oxidizer transport. A kinetic analysis indicates that the dynamic competition between the reaction classes- (a) degenerate chain branching and (b) chain termination/propagation - along with continuous fuel and oxygen leakage through the flame location contributes to an oscillatory burning phenomena of ever-increasing amplitude. Analysis based on single full-cycle of oscillatory burning shows that the reaction progression matrices (evolution of heat and species) for QOOH➔chain propagation/termination reactions (here, Q = C 7 H 14 -) directly scales with the gas phase temperature field. On the contrary, the QOOH➔degenerate branching reactions undergoes three distinct stages within the same oscillatory cycle. The coupled flame dynamics and kinetics suggest that in the oscillatory burning mode, kinetic processes dynamically cross through conditions characterizing the negative temperature coefficient (NTC) turnover temperature, separating low temperature and NTC kinetic regimes. In addition, a parametric study is conducted to determine the role of O 3 seeding level on the observed oscillation phenomena.
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#1Fahd E. Alam (USC: University of South Carolina)H-Index: 4
#2Sang Hee Won (USC: University of South Carolina)H-Index: 3
Last.Tanvir Farouk (USC: University of South Carolina)H-Index: 17
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#1Christopher B. Reuter (Princeton University)H-Index: 7
#2Minhyeok Lee (Princeton University)H-Index: 2
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#1Sili Deng (Princeton University)H-Index: 6
#2Dong Han (Princeton University)H-Index: 11
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#1Vedha Nayagam (Case Western Reserve University)H-Index: 4
#2Daniel L. Dietrich (Glenn Research Center)H-Index: 13
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#1Daniel L. Dietrich (Glenn Research Center)H-Index: 13
#2Vedha Nayagam (Case Western Reserve University)H-Index: 4
Last.Yu Cheng Liu (Cornell University)H-Index: 10
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#1Guenter Paczko (RWTH Aachen University)H-Index: 2
#2N. Peters (RWTH Aachen University)H-Index: 56
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Cited By1
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#2Christopher B. Reuter (Princeton University)H-Index: 7
Last.Sang Hee Won (USC: University of South Carolina)H-Index: 3
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#1Mohammadhadi Hajilou (UW: University of Wyoming)H-Index: 2
#2Matthew Q. Brown (UW: University of Wyoming)
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