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Investigation of Extinguishment by Thermal Agents Using Detailed Chemical Kinetic Modeling of Opposed Jet Diffusion Flames.


pdf icon Investigation of Extinguishment by Thermal Agents Using Detailed Chemical Kinetic Modeling of Opposed Jet Diffusion Flames. (948 K)
Pitts, W. M.; Blevins, L. G.

NISTIR 6588; November 2000.

U.S./Japan Government Cooperative Program on Natural Resources (UJNR). Fire Research and Safety. 15th Joint Panel Meeting. Volume 1. Proceedings. March 1-7, 2000, San Antonio, TX, Bryner, S. L., Editor(s), 242-249 pp, 2000.

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Keywords:

fire safety; fire research; jet flames; diffusion flames; extinguishment; thermal agents; reaction kinetics

Abstract:

Thermal fire-fighting agents are being investigated as potential replacements for halons which can no longer be manufactured due to their deleterious effects on stratospheric ozone. This work describes a detailed chemical kinetic modeling study of methane planar opposed jet laminar diffusion flames burning in air diluted with various thermal agents. Extinction conditions are characterized as a timction of agent concentration. Comparison of the calculated results for burning in nitrogen-diluted air with literature values for the extinguishing concentration allows the corresponding maximum flame temperature at extinguishment to be estimated as 1550 K. By applying this criterion, extinguishing concentrations are calculated for argon, helium, carbon dioxide, and water vapor. Calculated values are shown to be in good agreement with measurements in cup burners using heptane fuel. Surrogate agents having non physical behaviors have been used to characterize particular aspects of flame extinguishment by thermal agents. It is shown that dilution effects result from passage of oxygen through the flame front and that these effects should be accounted for when estimating the amount of a particular thermal agent required to extinguish a flame. By the use of a surrogate agent which absorbs heat by unimolecular reaction, it is demonstrated that the physical location of the heat extraction relative to the flame front does not modify the effectiveness of a thermal agent as long as the agent is subsequently convected into the flame zone.