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Combustion Models for Wooden Brands.


pdf icon Combustion Models for Wooden Brands. (1413 K)
Woycheese, J. P.; Pagni, P. J.

International Conference on Fire Research and Engineering (ICFRE3), Third (3rd). Proceedings. Society of Fire Protection Engineers (SFPE), National Institute of Standards and Technology (NIST) and International Association of Fire Safety Science (IAFSS). October 4-8, 1999, Chicago, IL, Society of Fire Protection Engineers, Boston, MA, 53-71 pp, 1999.

Sponsor:

National Institute of Standards and Technology, Gaithersburg, MD

Keywords:

fire research; fire protection engineering; combustion models; wood; earthquakes; wildland urban interface; equations; fire plumes

Abstract:

Eight combustion models for burning brands are reviewed. An averaged stagnation-point burning model, using the chemical properties of wood, is used here. Maximum propagation distances are calculated for disk-shaped brands lofted in large fires, such as occur after earthquakes or at urban/wildland interfaces. Lofting in the fire plume and propagation downwind are approximated here with distinct flow fields: a Baum and McCaffrey model for the plume and a constant horizontal velocity driving downwind propagation. In the plume, the brands rise with maximum drag and no lift. During propagation, both lift and drag act on the brand. It is assumed to have a fixed angle of attack, 35 deg < alpha < 90 deg, with respect to the relative velocity vector. For these alpha, the disk lift and drag coefficients are C1 = 1.17cos(alhpa) and Cd = 1.17sin(alpha), so that lift increases with decreasing alpha. Analytical expressions for dimensionless propagation distance, height, and brand size are developed in terms of four dimensionless parameters: initial lofting height; constant horizontal wind; angle of attack; and dimensionless burning parameter.