Horizontal flame spread over thin solids in reduced buoyancy environments

A Horizontal Channel Apparatus (HCA) has been employed to investigate opposed flame spread over solid fuels in reduced buoyancy environments, which would be encountered at the diminished gravitational levels on extraterrestrial surfaces (e.g., the partial gravity on the Moon and Mars) as well. With a scaling analysis, the characteristic buoyant flow velocity in HCA is well correlated to the channel height and the Rayleigh ( Ra ) number. The experimental results show that, without forced flow, the flame spread rate and flammability in HCA can be correlated with those at different gravity levels by using Ra number, in-dicating HCA may have the ability to simulate the burning characters in partial gravity. Together with the Reynolds ( Re ) and Ra numbers, which signify the role of forced and buoyant flow, respectively, the flame spread rates and the map of flammability of the solid fuel obtained in the current HCA experiments are determined. Furthermore, four distinctively different flame spread patterns are found at various channel heights and opposed-flow velocities once the width of the cellulosic sample is extended. Likewise, the map of flame spread patterns is governed by the Re and Ra. It is further found through the examinations of the time average of the mass-loss rate that as long as Ra is below a critical value, the opposed flow in terms of Re mainly determines the oxygen transportation, while the reduced buoyancy in terms of Ra mainly contributes to the bifurcations of the potential hydro/thermal instabilities.(c) 2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved