Radiative Ignition and Transition to Spread Investigation (RITSI).
Radiative Ignition and Transition to Spread
Investigation (RITSI).
(1865 K)
Kashiwagi, T.; Olson, S. L.
NASA/CP-1998-207891;
Third United States Microgravity Payload: One Year
Report. Proceedings. February 10-11, 1997, Washington,
DC, 97-117 pp, 1998.
Sponsor:
National Aeronautics and Space Administration, Lewis
Research Center, Cleveland, OH
Keywords:
microgravity; flame spread; ignition; smoldering;
experiments; char; temperature; lamps
Abstract:
A total of 25 experiments was conducted in the Glovebox
Facility on the USMP-3 mission to study the behavior of
both flaming and smoldering ignition events, the
transition from ignition to flame/smoldering spread, and
the flame/smoldering growth pattern in air. Twenty-one
of the 25 experiments were flaming experiments and the
remainder were smoldering experiments. Ignition was
initiated by a heated wire across a thermally thin
filter paper in the middle of the sample for the
two-dimensional configuration and by a focused beam from
a halogen/tungsten lamp at the center of the sample for
the three-dimensional configuration. The external air
flow velocity was varied from 0 cm/s to 6.5 cm/s. The
ignition and subsequent flame spread events were
recorded by a video camera, a 35 mm camera, and 6
thermocouples (2 in the gas phase and 4 in the sample).
The results indicate that non-piloted radiative ignition
of the paper by external thermal radiation tends to
occur more easily than in normal gravity. In the
two-dimensional configuration, the transition from
ignition to downstream flame spread never occurred; only
the transition to upstream spread took place. In the
three-dimensional configuration, a char growth pattern
emerged in the shape of a fan, with the ignited area as
the center of the fan and the fan spreading in the
upstream direction. The internal angle of the fan
increased with an increase in external flow velocity
(higher flow velocity gave a more opened fan pattern).
At an external flow velocity of 5 cm/s, the flame was
horseshoe-shaped and the char pattern became an
elongated semicircle toward upstream. It appears that
the peak upstream flame spread rate was reached at a
higher external velocity than for the two-dimensional
flame front. Flame spread much faster along open edges
of the sample paper than along the sample face,
presumably due to there being larger supply of oxygen
and energy feedback at the open edges than at the
surface. These results indicate the possible importance
of the effect of the flame front shape such as the
curvature of the flame front on spread rate and flame
strength. A complex, unexpected finger-shaped char
growth pattern was observed during the smoldering
experiment. Higher external flow velocity increased the
number of localized smoldering fronts, of the char
fingers they left behind, and frequency of bifurcations
from the fingers. At present, it is not clear what
caused such a complex char growth pattern.
