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Flame Extinguishment in a Cup-Burner Apparatus.


pdf icon Flame Extinguishment in a Cup-Burner Apparatus. (430 K)
Takahashi, F.; Linteris, G. T.; Katta, V. R.

E4 - Fire Research IV/Paper E21;

Combustion Institute/Western States, Central States and Eastern States. Fourth (4th) Joint Meeting of the U.S. Sections. Hosted by The Eastern States Section of the Combustion Institute and Drexel University. E4 - Fire Research IV/Paper E21. March 20-23, 2005, Philadelphia, PA, 1-6 pp, 2005.

Keywords:

combustion; burners; flame extinguishment; laminar flames; diffusion flames; gravity; fire extinguishing agents; extinguishment; flame temperature; heat capacity; flame structures

Abstract:

Unsteady extinguishment phenomena of laminar methane-air co-flow diffusion flames formed in a cup-burner apparatus at normal earth gravity have been studied experimentally and computationally. A gaseous fire-extinguishing agent (CO2, N2, He, Ar, or CF3H) was introduced gradually into a coflowing oxidizer stream until blowoff-type extinguishment occurred. The agent concentration in the oxidizer required for extinguishment was nearly independent of a wide range of the mean oxidizer velocity, exhibiting a so-called plateau region, for all agents except helium. Numerical simulations with detailed chemistry were performed to reveal the detailed flame structure and to predict the minimum extinguishing concentration (MEC) of agent at a fixed oxidizer velocity for a comparison with the experiment previously conducted. The MEC values of agents determined were: experiment: CF3H, (11.7 - 0.8)%; CO2, (15.7 - 0.6)%; N2, (25.9 - 1.0)%; He, (26.7 - 1.1)%; and Ar, (37.3 - 1.5)%; computation: CF3H, 10.1%; CO2, 14.5% (or 16.1% with different kinetic parameters for a methyl-H atom reaction step); N2, 25.2%; He, ~23%; and Ar, 35.7%. Despite the complexity of chemistry and flame-flow interactions in the blowoff processes, the numerical predictions of MECs were generally in good agreements (~6% less, on average) with the measurements. The relative ranking of the MECs depended upon primarily a reverse order of the heat capacity of the agent-laden oxidizers for all of the inert agents tested.