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Fire Propagation in Concurrent Flows. Annual Progress Report. September 1, 1991-August 31, 1992.


pdf icon Fire Propagation in Concurrent Flows. Annual Progress Report. September 1, 1991-August 31, 1992. (947 K)
Fernandez-Pello, A. C.

Annual Progress Report; 17 p. 1993.

Sponsor:

National Institute of Standards and Technology, Gaithersburg, MD

Keywords:

fire spread; gas flow; oxygen concentration; experiments; turbulent flow; laminar flow

Abstract:

A research program is being conducted to study the mechanisms controlling the spread of fire in oxidizing gas flows moving in the direction of flame propagation. During this reporting period research has been conducted to study concurrent flame spread under varied oxygen concentrations, with emphasis on vitiated conditions. Experiments have been completed with laminar flow, and are currently underway in turbulent flow. The parameters varied in the experiments are the oxidizer flow velocity, turbulence intensity and oxygen concentration, and the geometrical orientation (floor and ceiling). Their effect on the flame spread process is studied by measuring the rate of flame spread, flame length, surface heat flux, products of combustion and soot. Experiments are conducted with thick PMMA sheets as fuel and mixtures of oxygen nitrogen as oxidizer. The results of the experiments show that at low oxygen concentrations, the flame spread rate increases almost linearly as the flow velocity or oxygen concentration is increased. For high oxygen concentrations, the dependence of the spread rate on the oxygen concentration follows a second power law. By comparing the floor and ceiling results it is found that buoyancy has two opposite effects, one is enhancing the heat transfer to the surface by reducing the flame stand-off distance and the other reducing the chemical reaction completeness by intensifying the flame quenching at the wall. The overall buoyancy effect on the flame spread and mass burning processes depends on the flow condition.