Effects of Slow Wind on Localized Radiative Ignition and Transition to Flame Spread in Microgravity.
Effects of Slow Wind on Localized Radiative Ignition and
Transition to Flame Spread in Microgravity.
Kashiwagi, T.; McGrattan, K. B.; Olson, S. L.; Fujita,
O.; Kikuchi, M.; Ito, K.
Combustion Institute, Symposium (International) on
Combustion, 26th. Proceedings. Volume 1. July
28-August 2, 1996, Napoli, Italy, Combustion Institute,
Pittsburgh, PA, 1345-1352 pp, 1996.
combustion; flame spread; ignition; microgravity; lamps
An experimental and numerical investigation of ignition
and the subsequent transition to flame spread over a
thermally thin cellulosic sample is described. The
experiments were conducted using a lamp as an external
radiant source in a 50% oxygen atmosphere at three
different wind velocities of 0, 2, and 5 cm/s in a 10s
drop tower. The results show that there are no
significant effects of the slow wind on the
ignition-delay time. Photographic sequences of both the
experiments and the calculations show that the wind
increases the flame propagation speed in the upwind
direction, while decreasing it in the downstream
direction. The downstream flame fails the transition to
flame spread and becomes a tail of the upstream flame.
The downstream char front propagates much slower than
that for the upstream direction. Three-dimensional,
time-dependent numerical solutions to the Navier-Stokes
equations are used to simulate the experiments. Three
global degradation reactions describe the pyrolysis of
the sample paper, and one gas phase reaction describes
the combustion ofthe fuel gases. The model results
reflect the quanlitative features of the experiments and
also are in reasonable quantitative agreement, given the
uncertainty of the gas phase reaction mechanism.