Spring 2021 Meeting of the APS Ohio-Region Section
Volume 66, Number 3
Friday–Saturday, April 9–10, 2021;
Virtual Meeting Hosted by John Carroll University, Cleveland Heights, OH; Time Zone: Eastern Daylight Time, USA
Session B05: Plenary Talk III
10:00 AM–11:00 AM,
Saturday, April 10, 2021
Chair: Naveed Piracha, John Carroll University
Abstract: B05.00001 : Cool flames and hot flames: Combustion experiments onboard the International Space Station
10:00 AM–11:00 AM
Preview Abstract
Author:
Vedha Nayagam
(Department of Mechanical and Aerospace Engineering Case Western Reserve University, Cleveland, Ohio)
Combustion experiments are conducted onboard the International Space Station
(ISS) to study the flammability of condensed phase fuels, and to understand
the fundamental aspects of diffusion flames in the absence of buoyancy.
Recent droplet combustion experiments (FLEX -- Flame Extinguishment
Experiments) performed in the ISS have led to the discovery that certain
fuel droplets, following radiative extinction of visible hot flames, can
support quasi-steady burning without a visible flame, controlled by
low-temperature chemistry (aka, cool flames). When the cool flame
extinguished at a finite droplet diameter a condensation vapor cloud was
found to form surrounding the droplet.
These cool flames require relatively long residence times to burn and
buoyancy-limited earthbound experiments do not provide sufficient residence
time for this phenomenon to develop -- limiting the ability to study the
phenomena in terrestrial laboratories. Theoretical studies show that that
the cool flames are formed in the negative temperature coefficient (NTC)
region of the n-alkane chemistry where the chemical reactivity decreases
with increasing temperature. The analysis further shows that cool-flame
extinction is a chemical-kinetic/heat-transfer instability phenomenon,
instead of the conventional hot-flame extinction caused competition between
heat release and the rate of diffusive energy loss through heat conduction.
These findings have many potential applications on earth. The next
generation engine technologies, such as the homogeneous charge compression
ignition (HCCI) engine, or the reactivity controlled compression ignition
(RCCI) engine, can benefit from the improved understanding brought about by
this discovery. Other areas of application include fuel reformulation and
production of hydrogen from gasoline for use in fuel cells. Another area of
importance lies in questions about fire safety in space vehicles. Since the
cool mode of droplet combustion persists after hot-flame extinction, safety
procedures based only on considerations of hot flames may be inadequate for
assuring safety under all conditions.