Journal
PROCEEDINGS OF THE COMBUSTION INSTITUTE
Volume 36, Issue 2, Pages 2531-2539Publisher
ELSEVIER SCIENCE INC
DOI: 10.1016/j.proci.2016.08.019
Keywords
Low-temperature chemistry; Cool flame; Extinction; Microgravity; Droplet
Funding
- NASA Space Life and Physical Sciences Research and Applications Program
- International Space Station Program
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A recent set of experiments carried out onboard the International Space Station (ISS) have shown that large n-alkane droplets, after the radiative extinction of the visible flame, can burn quasi-steadily in a low-temperature regime, up to a diffusive extinction accompanied by the formation of a vapor cloud. The experiments have also demonstrated that small droplets are unable to exhibit radiative extinction, but instead burn to completion or disruptively extinguish. In this work, we applied a mathematical model able to reproduce the experimental data in terms of vaporization rates, standoff ratios, extinction diameters. A detailed kinetic mechanism (with similar to 450 species and similar to 17,000 reactions) was taken into account, in order to correctly reproduce the low-temperature combustion regime. The role of several parameters (initial diameter of the droplet, composition of the gaseous environment, and pressure) on the extinction of the hot-temperature flames was numerically investigated. Predictions are found in good agreement with experimental measurements, showing that only droplets with an initial diameter larger than a critical diameter undergo radiative extinction. A linear relationship between the squared critical diameter and the molar fraction of oxygen in the atmosphere was found and demonstrated on the basis of scaling arguments. (C) 2016 by The Combustion Institute. Published by Elsevier Inc.
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