Assessing Halon Alternatives for Aircraft Engine Nacelle Fire Suppression

Abstract

A coaxial turbulent spray burner was built to evaluate the relative effectiveness of different chemicals for suppressing fires in a jet engine nacelle. The fire suppressant of current choice, halon 1301 (CF3Br), must be replaced because of its detrimental effect on the ozone layer. The alternatives being considered lack the chemical activity of CF3Br, so that the ability of the agents to mix into the flame convectively and to absorb heat is critical to their success. An agent delivery system was designed to inject the desired amount of material into the air upstream of a fuel nozzle and to control the agent injection rate through variation of the storage pressure and the duration of time that a solenoid valve remains open. The influence of air velocity, fuel flow, and injection period on the amount of nitrogen required to extinguish a jet fuel spray flame is discussed. The effectiveness of eleven different fluorocarbons, hydrofluorocarbons, and hydrochlorofluorocarbons is compared to that of halon 1301. The alternatives required 1.7 to 2.3 times the amount (on a mass basis) of CF3Br to extinguish the spray flame, with HCFC-22 being the most efficient and FC-31-10 the least.