A comparison of direct methods to determine n -th order kinetic parameters of solid thermal decomposition for use in fir
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A comparison of direct methods to determine n-th order kinetic parameters of solid thermal decomposition for use in fire models Richard E. Lyon • Natallia Safronava
Received: 26 March 2012 / Accepted: 17 December 2012 Ó Akade´miai Kiado´, Budapest, Hungary 2013
Abstract Pyrolysis models for burning solids in fire simulations are sensitive to the values of the activation energy, frequency factor, and reaction order that characterize the thermal decomposition of the solid to gaseous fuel, so direct measurement of these kinetic parameters is recommended, and simple methods are preferred. Three direct methods were evaluated with regard to the ability of their kinetic parameters to reproduce the thermal decomposition of five polymers measured by differential thermogravimetric analysis using the reaction order model. It was found that the two multiple heating rate methods produced identical, physically based kinetic parameters, while the peak property method produced non-physical kinetic parameters. However, all of these kinetic parameters in a single-step reaction order model gave reasonably good conversion histories for non-charring and moderately charring polymers. For a highly charring polymer, the conversion histories were poorly described without a multiple step reaction. The temperature at the maximum rate of conversion was found to be essentially independent of the reaction order, which decouples the frequency factor from the reaction order in the direct kinetic methods. Any of the direct methods are sufficiently accurate to obtain kinetic parameters for pyrolysis models because of the inherent spatial and temporal averaging of reaction rates at the burning surface of a thick solid and the uncertainty in the heat
R. E. Lyon (&) N. Safronava Federal Aviation Administration, William J. Hughes Technical Center, Atlantic City International Airport, Pomona, NJ 08405, USA e-mail: [email protected] N. Safronava Technology and Management International, LLC, 1433 Hooper Avenue, Suite 330, Toms River, NJ 08753, USA
transfer mechanisms and thermo-physical parameters used in the models. Keywords Kinetics Pyrolysis Polymer Thermal decomposition Thermal analysis Fire model
Background The limitations of nonisothermal methods of thermal analysis for chemical kinetics of solids include the dependence of the kinetic parameter values on the reaction model, the error associated with predicting rates outside the experimental range of heating rates, and the difficulty of deriving mechanistic information [1–5]. However, nonisothermal methods are widely used and are appropriate for engineering fire models that seek to describe the burning rate of a solid during transient heating in a fire [6–18]. When solids burn, the temperature and heating rate decrease with distance away from the flaming surface, so the mass (fuel) flux is a spatial and temporal average of thermal decomposition (fuel generating) reactions occurring in-depth [6–18]. Simulations of the ignition and burning behavior of materials using pyrolysis mod
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