Suppression of Cup-Burner Flames.
Suppression of Cup-Burner Flames.
(1555 K)
Takahashi, F.; Linteris, G. T.; Katta, V. R.
Scale Modeling, 4th International Symposium (ISSM-IV).
International Symposium on Scale Modeling (ISSM).
Proceedings. September 17-19, 2003, Cleveland, OH,
45-54 pp, 2003.
Keywords:
fire suppression; flame stabilization; halon
alternatives; diffusion flames; flame structures; flame
extinction
Abstract:
The unsteady suppression process of a laminar
methane-air co-flow diffusion flame formed on a cup
burner has been studied experimentally and numerically
in normal earth gravity. The computation uses a
time-dependent direct numerical simulation with detailed
chemistry. A fire extinguishing agent (CO2 or CF3H) was
introduced into a coflowing oxidizer stream by gradually
replacing the air (the standard method) or the nitrogen
in the air (the constant oxygen concentration method).
The agent concentration required for extinguishment was
constant over a wide range of the oxidizer velocity,
showing a so-called plateau region. The measured
extinguishing volume fractions of the agents were: CO2
replacing air, (15.9 0.6)%; CF3H replacing air, (11.7
0.8)%; CO2 replacing N2, (40.2 2.0)%; and CF3H
replacing N2, (20.3 1.5)%. The cup-burner flame without
agent flickered at ~11 Hz or ~15 Hz, depending on the
oxidizer velocity. The flame base sometimes oscillated
at half the flickering frequency just before the flame
blew off. The suppression of cup-burner flames occurred
via a blowoff process (in which the flame base drifts
downstream) rather than the global extinction phenomenon
typical of counterflow diffusion flames. The numerical
simulations predicted the suppression limits and the
flickering frequency with good agreements with the
experimental observations and, more importantly,
revealed the detailed mechanisms of the flame-base
oscillation and subsequent blowoff phenomena.
