Suppression of Engine Nacelle Fires (NIST SP 890)

A series of experimental measurements were conducted and simple models were developed in an effort to provide an improved understanding of the influence of various parameters on the processes controlling flame stability in engine nacelle applications. The knowledge gained is compiled into usable tools which may assist suppression system designers determine the mass and rate of agent injection required for engine nacelle fire suppression. The Section is broken into several subsections. In Section 9.2, a description of the range of parameters which characterize engine nacelles is provided. The historical development of current halon 1301 fire protection systems is described. In Section 9.3, the results of four distinct experiments are discussed. First, the suppression effectiveness of candidate replacement agents (CF3I, C2HF5, and C3HF7) are tested on a turbulent jet spray flame. Second, suppression of a baffle stabilized pool fire is described. Third, measurements on the impact of the replacement agents on the ignition temperature of fuel/air/agent mixtures is discussed. Finally, measurements determining the flammability limits of propane/air/C2HF5 mixtures are discussed. The importance of agent entrainment into the recirculation/combustion zone of obstacle stabilized flames is emphasized. In Section 9.4, computational modeling of gaseous agent injection into a mock engine nacelle is described. The calculations are compared to measurements conducted in a wind tunnel. In Section 9.5, a simple algebraic model is developed which gives guidance on agent concentration requirements for flame suppression in generic nacelle configurations. Key findings and recommendations are compiled in Section 9.6. References are listed in Section 9.8.