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Experiments designed to measure kinetic rate constants of ignition of pulverized coals showed clearly that, for single particles or dilute suspensions, particle-to-particle variations due to reactivity and/or thermophysical properties are important. There exists ample evidence that the most important factor in interpreting these data is the existence of a variation in chemical reactivity in the sample. It is surprising, therefore, to note that all previous studies presumed that a single (average) activation energy is adequate to describe the ignition process. The equations formulated using this presumption are then correlated to the experimental measurements to infer the kinetic rate constants of ignition. The major objectives are to develop a model of heterogeneous ignition which allows for a distribution of activation energies, and to implement this model to interpret previously published data. It is the authors hypothesis that variations in chemical reactivity account for the experimental trends observed. Another objective of this project is to examine the effects of variations in thermodynamic and physical properties (e.g. specific heat, particle diameter, density) on data interpretation from previous ignition experiments. An attached paper submitted for review to ``Combustion and Flame`` summarizes the Distributed Activation Energy Model of Ignition, which accounts for particle-to-particle variations in reactivity within a sample by allowing for a distribution in activation energies among the particles and a single preexponential factor. The model captures the main characteristics of actual experiments, namely (1) the gradual increase in ignition frequency with increasing gas temperature and (2) the variation of the slope of the ignition frequency with O{sub 2} concentration. Finally, it has been shown that adjustments to the model parameters can be used to fit experimental data and extract reaction rate constants

A distributed activation energy model of heterogeneous coal ignition. Technical progress report, April 1-- June 30, 1995