Extinction Characteristics of Cup-Burner Flame in Microgravity.
Extinction Characteristics of Cup-Burner Flame in
Katta, V. R.; Takahashi, F.; Linteris, G. T.
AIAA 2003-1150; 12 p. 2003.
microgravity; extinction; flame extinction; fire
suppression; microgravity combustion; halon
alternatives; flame stabilization; carbon dioxide
Carbon dioxide extinguishes flames through dilution
process. The extinction characteristics of CO2 were
previously studied using a cup-burner flame under
normal-gravity conditions. As the diffusion flames
behave differently in microgravity compared to those on
earth, it is important to understand the structure of
cup-burner flame and the extinction characteristics of
CO2 for 0g conditions. A numerical study was performed
in the present paper using a time-dependent,
axisymmetric mathematical model and by incorporating
detailed chemical kinetics of CH4 and O2. Calculations
were performed for the cup-burner flame under different
gravitational forces. It was observed that the
cup-burner flame ceases to flicker under gravitational
forces less than 0.5g. As the buoyancy force was
reduced, the flame diameter increased, the tip of the
flame opened, and the flame at the base became vertical.
Through numerical experiments it was found that
radiative heat loss was solely responsible for the
extinction of flame in the tip region under 0g
conditions. In contrast, 1g flames were not affected
much by the radiative heat losses. Calculations were
made by adding CO2 to air stream to obtain the limiting
volume fraction of CO2 for extinguishing the 0g flame.
Similar to that observed in 1g flames, addition of CO2
destabilized the flame base, which then moved downstream
in search of a new stabilization location. For CO2
volume fractions greater than 19.1%, the flame base
moved out of the computational area, as it could not
find a stabilization point within the domain. This
limiting concentration for 0g flame is ~ 32% higher than
that obtained for the same flame under normal-gravity
conditions. Calculations made by ignoring radiation for
the limiting flame under 0g conditions yielded a stable
flame. This study suggested that it is important to
consider radiation while estimating the extinction
limits of cup-burner flames in microgravity.