Numerical Investigations of CO2 as Fire Suppression Agent.
Numerical Investigations of CO2 as Fire Suppression
Agent.
(661 K)
Katta, V. R.; Takahashi, F.; Linteris, G. T.
Fire Safety Science. Proceedings. Seventh (7th)
International Symposium. International Association for
Fire Safety Science (IAFSS). June 16-21, 2003,
Worcester, MA, Intl. Assoc. for Fire Safety Science,
Boston, MA, Evans, D. D., Editor(s), 531-542 pp, 2003.
Keywords:
fire research; fire suppression; carbon dioxide; pool
fires; flame extinction; diffusion flames; mathematical
models
Abstract:
Understanding suppression mechanisms of different
fire-suppressing agents including CF3Br (Halon 1301) and
inert gases is useful for their efficient use and for
developing new agents. Because of the similarities
between unsteady jet diffusion flames formed over the
cup burner and uncontrolled fires, it is believed that
studies of fire-suppressing agents in the former system
could provide valuable information on the behavior of
such agents in actual fires. In the present study,
suppression characteristics of CO2 were investigated in
two flame systems: 1) a periodically oscillating,
methane-air jet diffusion flame formed over a cup
burner, and 2) a steady-state planar flame formed
between opposing jets of fuel and air. A detailed
chemical-kinetics model having 31 species and 346
elementary-reaction steps was used. Calculations made
for the cup burner yielded a flame-flicker frequency of
about 10 Hz. The suppression mechanisms promoted by CO2
were investigated by adding CO2 to the airflow, while
maintaining the total flow rate constant, for both the
cup-burner and opposed-jet flames. In the cup-burner
flame, the addition of CO2 reduced the flame temperature
to ~1620 K at suppression. Addition of CO2 destabilized
the flame base, which then moved downstream in search of
a new stabilization location. For CO2 volume fractions
greater than 14.5%, the flame base moved out of the
computational area, as it could not find a stabilization
point within this domain. The unsteady flickering motion
of the flame and higher concentrations of CO2
accelerated this quenching process through blowout. Even
for very high concentrations of CO2, the calculations
did not yield simultaneous quenching of the entire
cup-burner flame. On the other hand, the opposed-jet
flame was extinguished through the global extinction of
flame chemistry. The low-strain (30 s-1) opposed-jet
flame extinguished for CO2 volume fractions > 16.4%,
while the moderately strained (90 s-1) flame
extinguished for volume fractions > 10.4%. Both the
opposed-jet flames extinguished nearly at the same flame
temperature (~1580 K), indicating that the extinction
limits in these flames are primarily controlled by
chemical kinetics.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899