Suppression of a non-premixed flame behind a step

Because of its many positive attributes, halon 1301, or trifluorobromomethane (CF3Br), has been used as a fire extinguishing agent in many applications, including aircraft, ships, and specialized structures. Due to its high ozone depletion potential, however, world-wide production was halted in 1994. In the search for a long-range replacement, novel types of extinguishing agents and delivery mechanisms are under development. To gauge the suitability of a replacement agent, methods are needed to evaluate the material's suppression effectiveness under conditions that relate to field applications. In this study, a laboratory-scale facility has been developed to screen the suppression effectiveness of agents that are delivered in a transient fashion, such as solid propellant gas generators. The facility features a pool fire stabilized behind an obstruction, which is known to be a highly challenging suppression configuration. The character of the flame and the impact of the air flow, propane flow, obstruction geometry, and rate of agent addition on the amount of material needed for suppression are examined for N2 and CF3Br. The impact of the injection process on the flowfield and the transport of the agent downstream are examined. A simple mixing model is useful to explain the observed trend of decreasing suppressant mass fraction with increasing injection duration, even for agents as different as CF3Br and N2. Direct numerical simulation of the suppression event is shown to successfully predict the quantity and rate of N2 required to extinguish the flame based upon a published global reaction rate for premixed propane/air flame propagation.