Dimensional Effects on the Transition From Ignition to Flame Spread in Microgravity.
Dimensional Effects on the Transition From Ignition to
Flame Spread in Microgravity.
Mell, W. E.; Kashiwagi, T.
Combustion Institute, Symposium (International) on
Combustion, 27th. Proceedings. Volume 2. August 2-7,
1998, Boulder, CO, Combustion Institute, Pittsburgh, PA,
2635-2641 pp, 1998.
combustion; microgravity; flame spread; ignition
Three-dimensional (3-D) and two-dimensional (2-D)
simulations of the transition from radiative ignition on
a solid fuel to flame spread in a imposed wind were
performed in microgravity. Two-dimensional flames were
found to quench (due to poor oxygen supply) more easily
(i.e., at larger wind speeds) than 3-D flames. Results
from the 2- and 3-D simulations were compared during the
transition phase at wind speeds that ultimately lead to
quenching of the 2-D flame but survival of the 3-D
flame. In all locations near and in the flame, oxygen
mass flux was larger in the 3-D flames and dominated by
diffusion (as opposed to convection). Oxygen was
supplied to the core of the 3-D flame due to diffusion
from the sides of the flame (in a cross-wind direction).
Diffusion in the 2-D flame was limited to directions
parallel to the wind. This cross-wind diffusion was most
significant at early times during transition when the
flame was small and had a relatively large curvature.
The 3-D flame, therefore, required less oxygen supply
from an external wind to undergo transition to flame
spread. Once flame spread was established there was
little difference between the 3-D flames (in the
centerline plane) and 2-D flames, due to the decreased
curvature of the three-dimensional flame relative to the
curvature during ignition and transition.