Enclosure Effects on Flame Spread Over Solid Fuels in Microgravity.
Enclosure Effects on Flame Spread Over Solid Fuels in
Microgravity.
(367 K)
Nakamura, Y.; Kashiwagi, T.; McGrattan, K. B.; Baum, H.
R.
Combustion and Flame, Vol. 130, No. 4, 307-321,
September 2002.
Keywords:
solid fuels; flame spread; microgravity; enclosures;
ignition
Abstract:
Enclosure effects on the transition from a localized
ignition to subsequent flame growth over a thermally
thin solid fuel in microgravity are numerically
investigated by solving the low Mach number
time-dependent Navier-Stokes equations. The numerical
model solves the two and three dimensional,
time-dependent, convective/diffusive mass, and heat
transport equations with a one-step global oxidation
reaction in the gas phase coupled to a three-step global
pyrolysis/oxidative reaction system in the solid phase.
Cellulosic paper is used as the solid fuel and is placed
in a slow imposed flow parallel to the surface. Ignition
is initiated across the width of the sample or at a
small circular area by an external thermal radiation
source. Two cases are examined; an open configuration
(i.e., without any enclosure) and the case with the test
chamber used in our previous microgravity experiments.
Numerical results show that the upstream centerline
flame spread rate for the case with the enclosure is
faster than that for the case without any enclosure.
This is due to the confinement of the flow field and
also thermal expansion initiated by heat and mass
addition in the chamber. The confinement accelerates the
flow in the chamber, which enhances oxygen transport
into the flame. In the three-dimensional configuration
with the spot ignition, the flame growth in the
direction perpendicular to the flow is significantly
enhanced by the confinement effects. The effect of the
enclosure is most significant at the slowest flow
condition investigated and the effect becomes less
important with an increase in imposed flow velocity. The
total heat release rate from the flame during a flame
growth period increases significantly with the
confinement and the enclosure effects should be
accounted to avoid underestimating fire hazard in a
spacecraft.
