Interaction of HFC-125, FC-218 and CF3I With High Speed Combustion Waves.
Interaction of HFC-125, FC-218 and CF3I With High Speed
Combustion Waves.
(670 K)
Grosshandler, W. L.; Gmurczyk, G. W.
Alliance for Responsible Atmospheric Policy; U.S.
Environmental Protection Agency; Environment Canada;
United Nations Environment Programme; U.S. Department of
Agriculture. Stratospheric Ozone Protection for the
90's. 1995 International CFC and Halon Alternatives
Conference and Exhibition. Proceedings. October 21-23,
1995, Washington, DC, 635-643 pp, 1995.
Sponsor:
Air Force Flight Dynamics Lab., Wright-Patterson AFB
Keywords:
combustion waves; halon alternatives; fire suppression;
detonation; aircraft fires; military aircraft; halons
Abstract:
Live-fire, full-scale testing has been conducted at
Wright-Patterson Air Force Base to identify an agent to
replace CF3Br (halon 1301) for suppressing fires in
military aircraft dry bays. The three chemicals being
considered (HFC-125, FC-218 and CF3I) had been evaluated
in a previous laboratory study, in which unique
properties of each chemical were identified in
small-scale experiments. The CF3I required the least
mass to suppress a turbulent spray flame but performed
less well in suppressing a quasi-detonation. FC-218
performed the best in the presence of a
quasi-detonation. HFC-125 was recommended previously as
a candidate because of its superior dispersion
characteristics; however, this chemical produced large
over-pressures in the deflagration/detonation tube. The
high pressures motivated the current study to determine
the initial conditions which would lead to dangerous
situations, and to explore a less extreme regime more
representative of a realistic threat. The
deflagration/detonation tube was lengthened from 7.5 to
10 m, the spiral insert in the test section was removed,
and the fuel was switched from ethene to propane to
produce uninhibited pressure ratios below 9:1 and
turbulent flame speeds between 300 and 600 m/s. Based
upon over a hundred experiments with the modified
facilty, it was possible to reconfirm the conclusion
that FC-218 provides the most consistent performance
over the widest range of fuel/air mixtures and tube
geometries. The CF3I has the greatest positive impact
at low partial pressure fractions, but exhibits
non-monotonic behavior of flame speed and shock pressure
ratio at increasing concentrations. The dangerously
high over-pressures previously exhibited by HFC-125 were
not observed during suppression under more moderate (and
realistic) combustion conditions. Considering these
results alone, all three agents remain viable candidates
for dry-bay applications.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899