An analysis of the sensitivity of the rate of buoyancy-driven flame spread on a solid material to uncertainties in the pyrolysis and combustion properties. Is accurate prediction possible?

Published

August 1, 2023

Author(s)

Yan Ding, Isaac Leventon, Stanislav Stoliarov

Abstract

An upward, buoyancy-driven flame spread on combustible solids is frequently the dominant contributor to the growth of fire in built environment. Thus, an ability to accurately predict the development of a fire is strongly linked to the accuracy of flame spread modeling, which requires knowledge of a wide range of properties that serve as model inputs. In this study, the sensitivity of flame spread dynamics to variation in these properties was examined to determine which properties carry measurement uncertainties that translate into the largest errors in the flame spread predictions. Upward flame spread on a solid material in a vertical corner configuration was simulated with two widely used computational tools, ThermaKin2Ds and Fire Dynamics Simulator (FDS). The sensitivity of fire growth to variations in material properties is examined in order to understand the relative importance of the knowledge of these properties. The nominal value of each material property was calculated as the average of measured values of a balanced set of 26 materials that represent the combustible polymeric solids widely used in industrial, transportation, and construction applications. The upper and lower boundaries of each property were defined based on an uncertainty quantification of each specific measurement. A measure of average flame spread velocity, (V_p ) ̅, was defined (based on the time derivative of pyrolysis front location) as the model output to characterize the flame spread dynamics. Overall, ThermaKin2Ds and FDS simulations are consistent, generally demonstrating similar sensitivity to model inputs. For both simulation tools, uncertainties in reaction kinetics (E_a/ln⁡(A)) and the heat capacity of the virgin material, c_virgin, had the most significant effect on calculated fire growth rate (the maximum magnitude change is 86%). FDS simulations also demonstrated a strong sensitivity to uncertainties in measured heat of combustion (approximately twice as sensitive as ThermaKin2Ds results). Variations in c_char, a_virgin, and ε_char showed negligible impact on predicted (V_p ) ̅, which indicates that these parameters are measured with sufficient accuracy to deliver reasonably accurate predictions of flame spread dynamics. This work enables the identification of the properties that should be measured with additional accuracy to provide meaningful predictions of flame spread dynamics.

Citation

Combustion and Flame

Pub Type

Journals

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Keywords

FDS, material properties, pyrolysis, sensitivity analysis, ThermaKin2Ds, upward flame spread

Citation

Ding, Y. , Leventon, I. and Stoliarov, S. (2023), An analysis of the sensitivity of the rate of buoyancy-driven flame spread on a solid material to uncertainties in the pyrolysis and combustion properties. Is accurate prediction possible?, Combustion and Flame, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=934453 (Accessed September 26, 2024)