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Suppression of High Speed Flames and Quasi-Detonations.


pdf icon Suppression of High Speed Flames and Quasi-Detonations. (3475 K)
Gmurczyk, G. W.; Grosshandler, W. L.

NIST SP 890; Volume 1; Section 2; November 1995.

Fire Suppression System Performance of Alternative Agents in Aircraft Engine and Dry Bay Laboratory Simulations. Volume 1. Section 2, Gann, R. G., Editor(s), 9-75 pp, 1995.

Available from:

National Technical Information Service
Order number: PB96-117775

Keywords:

fire suppression; aircraft engines; nacelle fires; simulation; detonation; effectiveness; deflagration; experiments; combustion; ethane; propane; fuel/air mixtures; halon 1301; halon alternatives

Abstract:

A dry bay is a normally confined space adjacent to a fuel tank in which a combustible mixture and an ignition source could co-exist following penetration by an anti-aircraft projectile. They vary considerably in volume, typically being in the range of 0.2 to 3.0 m3. They are located in the wings and fuselage, and their shape is most often irregular. Aspect ratios up to 10:1 are not uncommon. The bays may or may not be ventilated, and are usually cluttered with electronic, hydraulic and mechanical components. Compared to the events leading to engine nacelle fire suppression, the required timing is two orders-of-magnitude faster for dry bay protection. The previous study using a deflagration/detonation tube was concerned with establishing a comprehensive experimental program to screen the performance of over a dozen agents. The experiments were designed to cover the range of conditions that might occur in a dry bay. Although actual measurements of fuel concentrations in a dry bay during live-fire testing have never been made, one could envision a worst-case situation in which the fuel is vaporized and partially premixed with the air just prior to ignition, producing a rapidly moving turbulent flame. If the suppressing agent were not well mixed and the dry bay geometry were conductive, the turbulent flame could accelerate, generating a shock wave ahead of it and transitioning to a detonation before encountering the agent. Ethene was chosen as the fuel in the previous study because it was known to detonate easier than many other hydrocarbons. This provided the most severe test for all the agents under conditions that were not duplicated in any of the other bench-scale studies. The specific objectives of the current research project are the following: (a) To determine the effectiveness of HFC-125, relative to FC-218, in suppressing high speed turbulent propane/air flames using the detonation/deflagration tube apparatus; (b) To determine the conditions in the detonation/deflagration tube (equivalence ratio, tube geomtery) which lead to excessive pressure build-up during suppression by HFC-125 of propane/air mixtures initially at room temperature and pressure; (c) To determine the effectiveness of CF3I, relative to FC-218, in suppressing high speed turbulent propane/air flames using the detonation/deflagration tube apparatus; (d) To recommend a ranking of the three agents for full-scale dry bay applications based upon the current and previous suppression experiments.