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Gas Generator Induced Flow and Its Effect on Fire Flame Extinction.


pdf icon Gas Generator Induced Flow and Its Effect on Fire Flame Extinction. (3381 K)
Joulain, P.; Torero, J. L.

NIST GCR 98-745; 48 p. April 1998.

Sponsor:

National Institute of Standards and Technology, Gaithersburg, MD

Available from:

National Technical Information Service
Order number: PB98-146129

Keywords:

gas generators; flame extinguishment; fire suppression; test methods; solid propellants; flow fields; heat transfer; ignition; velocity measurement; walls

Abstract:

A limiting factor to the development of new suppression technology is the lack of appropriate screening methods. Among the new technologies that are intended to replace Halon 1301 are Solid Propellant Gas Generators (SPGG's), or flame suppressing gas generators. SPGG's are a spin-off from airbag technology and have demonstrated their ability to suppress certain types of fire, particularly aircraft engine nacelle and dry bay fires. To date there is no adequate screening method for SPGG's. The flow originating from burning a solid propellant reduces the Damkohler number by decreasing the residence time (high velocity flow of products) and increasing the chemical time (by directly altering the reactant concentrations, oxygen displacement effect). If the Damkohler number decreases below a critical value sudden extinction of the flame occurs. A facility that will serve to assess the performance of SPGG's has to be able to evaluate the combined effects of the gas discharge. Several alternatives have been proposed for an adequate flame and enclosure that will represent a "worst case" scenario for extinction and subsequent re-ignition. Among these alternatives is the recirculation zone induced by either a bluff body, a baffle, a backward facing step or a trench inside a wind tunnel. These configurations provide a controlled increase in the residence time, thus an increase in the Damkohler number. This report describes a preliminary evaluation of these configurations by means of a literature search and some preliminary computations using Large Eddy Simulation (LES) code developed at NIST.