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Numerical Investigations of CO2 as Fire Suppression Agent.


pdf icon 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.