Experimental and Numerical Evaluation of Metallic Compounds for Suppressing Cup-Burner Flames.
Experimental and Numerical Evaluation of Metallic
Compounds for Suppressing Cup-Burner Flames.
(934 K)
Linteris, G. T.; Katta, V. R.; Takahashi, F.
Combustion and Flame, Vol. 138, No. 1/2, 78-96, July
2004.
Keywords:
fire suppression; nanoparticles; flame inhibition;
diffusion flames; organometallics; flame structure; cup
burner; halon alternatives
Abstract:
The first tests of supereffective flame inhibitors
blended with CO2 have been performed in methane-air
laminar co-flow diffusion flames stabilized on a cup
burner. The CO2 volume fraction required to extinguish
the flames was determined for a range of added catalytic
inhibitor volume fractions. When added at low volume
fraction, the agents TMT, Fe(CO)5, and MMT were
effective at reducing the volume of CO2 required to
extinguish the flames, with performance relative to
CF3Br of 2, 4, and 8, respectively. This performance
advantage of the metallic compounds is less than that
determined in premixed or counterflow diffusion flames.
Further, as the volume fraction of each metallic
catalytic inhibitor was increased, the effectiveness
diminished rapidly. The greatly reduced marginal
effectiveness is believed to be caused by loss of active
gas-phase species to condensed-phase particles.
Laser-scattering measurements in flames with Fe(CO)5/CO2
blends detected particles both inside and outside (but
not coincident with) the visible flame location for
measurement points above the stabilization region. For
Fe(CO)5 addition to the air stream at 450 L/L, the peak
scattering cross section for vertically polarized light
was 1660 times the value for room-temperature air. The
first detailed numerical modeling studies were also
performed for methane-air cup-burner flames with CO2 and
Fe(CO)5 added to the oxidizer stream and are used to
interpret the experimental results. The role of
particles was also illustrated by the numerical results,
which showed that significant levels of supersaturation
exist in the flame for several of the important
iron-containing intermediates. This particle formation
is favored in the lower temperature stabilization region
of the cup-burner flames, as compared to the higher
relevant temperatures of previously described
counterflow diffusion flames. The results of this study
indicate that the appropriate flame configuration for
evaluating the effectiveness of some fire suppression
agents must be carefully considered, since in those
cases, different flame configurations can switch the
relative performance of an agent by an order of
magnitude.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899