FLAME EXTINGUISHMENT EXPERIMENT (FLEX)
Research Area: Combustion Science
Expedition(s): 18- 30
Principal Investigator(s): ● Forman A. Williams, PhD, University of California, San Diego,
La Jolla, California
RESEARCH OBJECTIVES
The Flame Extinguishment Experiment (FLEX)
examines the effectiveness of fire suppressants in
microgravity and quantifies the effect of different
possible crew exploration atmospheres on fire
suppression. The goal of this research is to provide
definition and direction for large-scale fire
suppression tests and to select the fire suppressant
for next-generation crew exploration vehicles.
EARTH BENEFITS
FLEX will help us understand combustion-generated
pollution and address fire hazards associated with
using liquid combustibles on Earth.
SPACE BENEFITS
FLEX will help us develop more efficient energy
production and propulsion systems on Earth and in
space.
RESULTS
Hot gases do not rise in microgravity, so an entirely different process called molecular diffusion
drives flame behavior. So far, researchers have seen some unexpected phenomena from FLEX
results. The most surprising discovery is the apparent continuous “burning” of heptane droplets
after flame extinction under certain conditions. First, the droplet undergoes normal transient
(short-lived) burning with a visible flame surrounding the droplet and extinguishes at a
relatively large droplet size. This event is followed by continuous, rapid, almost steady
vaporization of the droplet without the visible flame, which ends abruptly at a point called
“cool-flame extinction,” leaving behind a smaller droplet. It then either experiences normal
evaporation in the surrounding hot environment or grows slightly through condensation of the
vapor in the cloud that forms upon extinction or through migration of the vapor-cloud particles
ISS024M041721519 – In this NASA video capture, a
fuel droplet is dispensed on positioning wire prior to
being set aflame by ring-wire igniters during Flame
Extinguishment Experiments inside the Multi-user Drop
Combustion Apparatus.