Flame Extinguishment in a Cup-Burner Apparatus.
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.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899