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Transition From Localized Ignition to Flame Spread Over a Thin Cellulosic Material in Microgravity.

pdf icon Transition From Localized Ignition to Flame Spread Over a Thin Cellulosic Material in Microgravity. (307 K)
McGrattan, K. B.; Nakabe, K.; Baum, H. R.; Kashiwagi, T.

Combustion Institute/Eastern States Section. Chemical and Physical Processes in Combustion. Technical Meeting, 1993. October 25-27, 1993, Princeton, NJ, 409-412 pp, 1993.


National Aeronautics and Space Administration, Washington, DC


combustion; microgravity; ignition; flame spread; cellulosic materials; vapor phases


Ignition and flame spread processes are complicated by strong coupling between chemical reactions and transport processes, not only in the gas phase but also in the condensed phase. In most previous studies, ignition and flame spread were studied separately with the result that there has been little understanding of the transition from ignition to flame spread. In fire safety applications this transition is crucial to determine whether a fire will be limited to a localized, temporary burn or whether it will grow to become a large fire. In order to understand the transition to flame spread, the transient mechanisms of ignition and subsequent spread must be studied. However, there have been no definitive experimental or modeling studies because of the complexity of the buoyancy-induced flow near the heated sample surface. One must solve the full Navier-Stokes equations over an extended region to represent accurately the highly unstable buoyant plume and entrainment of surrounding gas. To avoid the complicated nature of the plume problem under normal gravity, previous detailed radiative ignition models were assumed to be one-dimensional or were applied at a stagnation point. Unfortunately, these models could not be extended to include the transition to flame spread.