Fire suppressant dispersion in a cold aircraft engine nacelle. (News Briefs).

Halon 1301 is the predominant fire suppressant used to extinguish aircraft engine-nacelle fires. Due to its adverse effect on the ozone layer, halon 1301 has been banned from production in the United States since 1994 in compliance with the Montreal Protocol on Substances that Deplete the Ozone Layer. NIST has since been extensively involved in the search for the replacements for halon 1301. Trifluoriodomethane (CF3I) has been proposed as a potential candidate for halon 1301 in aircraft engine nacelles.

One current focus at NIST is on the dispersion and distribution of CF3I at temperatures below its normal boiling point (-22 [degrees]C). Under such conditions, which are encountered during cold start of an aircraft engine on a cold tarmac or high-altitude cruising, there is a potential deterioration in the dispersion of the suppressant and its transport to the fire zone.

An engine nacelle simulator was built to conduct the research. The simulator, with observation windows and measurement ports, has a configuration and dimensions commensurate with a typical small engine nacelle. To simulate low temperature conditions, the entire facility was housed inside a large environmental test chamber in the U.S. Army CECOM Research, Development and Engineering Center at Fort Belvoir, and the suppressant discharge experiments were performed inside the chamber. The dispersion effectiveness of CF3I was assessed based on concentration measurements inside the engine-nacelle simulator using fast-response fiber-optic-based UV spectormeters. Discharge experiments at room temperature were also conducted to establish baselines for comparison.

The concentration measurements indicated that significant reduction in the dispersion effectiveness of CF3I occurred when it was used at temperatures below its normal boiling. Then a fire suppression system designed based on room-temperature test data may fail to provide adequate fire protection. Other parameters that could affect the dispersion and transport of the fire suppressant are currently being examined in our laboratory. Means to improve the performance of the fire suppressant in low temperature applications are also being explored. Extension to other high boiling-point liquid fire suppressants is being planned.

CONTACT: Jiann Yang, [phone]; [e-mail].