Suppression of Cup-Burner Flames Using Carbon Dioxide in Microgravity.
Suppression of Cup-Burner Flames Using Carbon Dioxide in
Microgravity.
(1236 K)
Katta, V. R.; Takahashi, F.; Linteris, G. T.
Combustion and Flame, Vol. 137, No. 4, 506-522, June
2004.
Keywords:
microgravity; carbon dioxide; burners; fire safety; fire
suppression; extinguishment; buoyancy; inhibitors
Abstract:
The extinguishment characteristics of CO2 as a
fire-suppressing agent have been studied experimentally
and numerically using a methane.air laminar co-flow
diffusion flame stabilized on a cup burner. Direct
numerical simulations of cup-burner flames under various
gravitational forces were performed using a
time-dependent, axisymmetric mathematical model with a
detailed-chemical-kinetic mechanism for CH4/O2
combustion. Experiments with cup-burner flames under
normal-gravity (1g) conditions were performed for
comparison purposes. Both the computed flicker frequency
and the predicted critical concentration of CO2 for
extinguishing the flame compared well with the
respective quantities measured in the experiments. As
the buoyancy force is reduced, the flicker frequency
decreases, the flame diameter increases, the tip opens,
and the base becomes vertical. It is predicted that the
cup-burner flame ceases to flicker for gravitational
forces corresponding to less than 0.5g. Numerical
experiments revealed that radiative heat loss is
predominantly responsible for flame quenching (opening)
in the tip region under microgravity (0g) conditions. In
contrast, 1g flames are affected only slightly by the
radiative heat loss. Calculations are made by adding
different amounts of CO2 to the air stream for obtaining
the critical volume fraction of CO2 to extinguish 0g
flames. The behavior is similar to that observed in 1g
flames: the addition of CO2 destabilizes the flame base,
which then moves downstream in search of a new
stabilization location. For CO2 volume fractions greater
than 19.1%, the flame base moves out of the
computational area, as it cannot find a stabilization
point within the domain. This critical concentration for
the 0g flames is ~32% higher than that computed for the
same flames under 1g conditions. Calculations made by
ignoring radiation for the limiting flame under 0g
conditions yielded a stable flame. This study suggests
that it is important to consider radiation heat losses
when estimating the extinguishment limits of cup-burner
flames in microgravity.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899