to the droplet surface. This
behavior is not explained by
conventional theories of droplet
combustion and is hypothesized
as a low-temperature chemical
reaction (cool flame) that
continues after the ‘hot’ flame
extinction. Cool flames typically
occur in premixed systems (this
is a diffusion flame), are
transient (this is quasi-steady),
and lead to a hot-flame ignition
(this is a hot-flame leading to a
cool flame that extinguishes),
which is a very unique
observation with very
significant theoretical and
practical implications.
Cool flames usually occur in premixed fuel systems where they are known to spread and
eventually lead to ignition that establishes hot-flame combustion, generating ignition pulses
commonly associated with engine-knocks in automobiles. Also, flames in space burn with a
lower temperature, at a slower rate, and with less oxygen than in normal gravity. This means
that materials used to extinguish fires in microgravity must be present in higher concentrations.
Through microgravity flame investigations scientists hope to gain a better knowledge of droplet
burning, improved spacecraft fire safety, and ideas for more efficient utilization of liquid fuels
on Earth (Nayagam 2012).
PUBLICATION(S)
Farouk TI, Hicks MC, Dryer FL. Multistage oscillatory “Cool Flame” behavior for isolated alkane
droplet combustion in elevated pressure microgravity condition. Proceedings of the Combustion
Institute. 2015;35:1701-1708. doi: 10.1016/j.proci.2014.06.015.
Shaw BD, Vang CL. Oxygen Lewis number effects on reduced gravity combustion of methanol
and n-heptane droplets. Combustion Science and Technology. 2016;188(1):150716065835002.
doi: 10.1080/00102202.2015.1072176.
Dietrich DL, Nayagam V, Hicks MC, et al. Droplet combustion experiments aboard the
International Space Station. Microgravity Science and Technology. October 2014;26:65-76. doi:
10.1007/s12217-014-9372-2.
Liu YC, Xu Y, Avedisian CT, Hicks MC. The effect of support fibers on micro-convection in droplet
combustion experiments. Proceedings of the Combustion Institute. August 2014;35(2):1709-
1716.
ISS019E015912 – Japan Aerospace Exploration Agency astronaut
Koichi Wakata, Expedition 19 flight engineer, works on the
Combustion Integrated Rack Multi-user Drop Combustion
Apparatus.