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Interaction of HFC-125, FC-218 and CF3I With High Speed Combustion Waves.


pdf icon Interaction of HFC-125, FC-218 and CF3I With High Speed Combustion Waves. (700 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.