Numerical prediction of flame spread over solid combustibles in a microgravity environment

Abstract

Abstract A computational model of three-dimensional, time-dependent flame spread in a microgravity environment is presented. The solid is assumed to be a thermally thin, pyrolysing cellulosic sheet. The gas-phase model includes the full Navier-Stokes equations with density and pressure variations and a six-flux model of radiation heat transfer. The solid phase model consists of continuity and energy equations whose solution provides boundary conditions for the gas phase equations. In the numerical procedure, the gas- and solid-phase equations are solved separately and iteratively at each time step. Predictions have been made of flame spread in slow forced flow under gravitational acceleration normal to the fuel surface and flame spread in a quiescent environment in an enclosed chamber under gravitational acceleration parallel to the fuel surface. Numerical simulations show that, under microgravity and slow-flow conditions, the flame spread process is highly unsteady with the upstream flame spreading faster than the downstream flame after a period of ignition. It has also been shown that the level of microgravity has a significant effect on the flame spread process.