Enclosure Effects on Flame Spread Over Solid Fuels in Microgravity
Y N. Nakamura, Takashi Kashiwagi, Kevin B. McGrattan
Enclosure effects on the transition from localized ignition to subsequent flame spread over a thermally-thin solid fuel in microgravity are investigated numerically 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 (two-dimensional configuration) or at a small circular area (three-dimensional configuration) by an external thermal radiation source. Two boundary conditions for the flow field are examined in the present study, an open configuration (i.e. without any enclosure) and a cold wall tunnel-like chamber. Numerical results show that the upstream flame spread rate is found to be faster within the enclosure. This is due to the flow-path confinement; acceleration of the flow in the chamber enhances oxygen transport into the flame, consequently the heat flux from flame to the surface increases as compared to the case without the enclosure. In the three-dimensional configuration, the flame spread in the direction perpendicular to the flow is significantly enhanced within the enclosure. The effect of the enclosure is found to be most significant at the slowest flow condition investigated. Calculated flame spread behavior induced by line ignition in the enclosure shows that flame spread is essentially three-dimensional and the flame shape tends to be curved where the effect of the enclosure is pronounced.
, Kashiwagi, T.
and McGrattan, K.
Enclosure Effects on Flame Spread Over Solid Fuels in Microgravity, Combustion and Flame, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=861101
(Accessed February 26, 2024)