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The role of cool-flame chemistry in quasi-steady combustion and extinction of n-heptane droplets

Published on Sep 3, 2014in Combustion Theory and Modelling1.654
· DOI :10.1080/13647830.2014.934296
Guenter Paczko2
Estimated H-index: 2
(RWTH Aachen University),
Norbert Peters57
Estimated H-index: 57
(RWTH Aachen University)
+ 1 AuthorsForman A. Williams54
Estimated H-index: 54
(UCSD: University of California, San Diego)
Abstract
Experiments on the combustion of large n-heptane droplets, performed by the National Aeronautics and Space Administration in the International Space Station, revealed a second stage of continued quasi-steady burning, supported by low-temperature chemistry, that follows radiative extinction of the first stage of burning, which is supported by normal hot-flame chemistry. The second stage of combustion experienced diffusive extinction, after which a large vapour cloud was observed to form around the droplet. In the present work, a 770-step reduced chemical-kinetic mechanism and a new 62-step skeletal chemical-kinetic mechanism, developed as an extension of an earlier 56-step mechanism, are employed to calculate the droplet burning rates, flame structures, and extinction diameters for this cool-flame regime. The calculations are performed for quasi-steady burning with the mixture fraction as the independent variable, which is then related to the physical variables of droplet combustion. The predictions with t...
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Recently, large diameter, isolated n-heptane droplet experiments under microgravity conditions (aboard the International Space Station) exhibited “Cool Flame” burning behavior, resulting from a heat loss mechanism that extinguishes hot combustion and a transition into a sustained, low temperature second stage combustion. In atmospheric pressure air, a single combustion mode transition to “Cool Flame” burning is followed by diffusive extinction. But with increasing pressure, multiple cycles of ho...
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