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Numerical Study of Thermal Decomposition and Pressure Generation in Charring Solids Undergoing Opposed-Flow Flame Spread.


pdf icon Numerical Study of Thermal Decomposition and Pressure Generation in Charring Solids Undergoing Opposed-Flow Flame Spread. (331 K)
Park, W. C.; Atreya, A.; Baum, H. R.

Volume 31; Part 2;

Combustion Institute, Symposium (International) on Combustion, 31st. Proceedings. Volume 31. Part 2. August 5-11, 2006, Heidelberg, Germany, Combustion Institute, Pittsburgh, PA, Barlow, R. S.; Sick, V.; Glarborg, P.; Yetter, R. A., Editor(s)(s), 2643-2652 pp, 2007.

Keywords:

combustion; fire research; flame spread; thermal decomposition; pressure; solids; wood; charring; char; pyrolysis; equations; mathematical models; conservation; kinetics; reaction kinetics; temperature

Abstract:

Thermal decomposition and pressure generation in charring solids undergoing opposed-flow flame spread have been numerically studied with a detailed physics-based model. The physical problem is modeled as a steady state two-dimensional process including three parallel finite rate reactions and volatiles convection. Local thermal equilibrium is assumed between char matrix and volatiles. For pressure calculation, the volatiles are assumed to follow the ideal gas law and Darcy's law. Numerical result indicates that the char density and product yields are functions of depth due to an insulating char layer. In addition, the characteristics of various simplifying assumptions such as global reaction, infinite rate kinetics and no convective gas transport have been investigated. The global reaction model shows excellent agreement on char layer thickness with the detailed model. However, it predicts higher pressure inside the charring solid. Infinite reaction rate model shows thicker char layer in the fore region and thinner char layer in the downstream region due to constant pyrolysis temperature. Also, it shows lower pressure in the char. Simplified energy model predicts thicker char and higher pressure than the detailed model.