#x2014;We derive two different asymptotic models which describe the nonsteady, nonplanar burning of certain types of homogeneous solid propellants. Motivated in part by recent work on ammonium perchlorate deflagration, we assume, in the first model, that a fraction of the pro-pellant is pyrolyzed directly to product gases at a solid/gas interface, while the remainder sublimes and burns in the gas phase. In the second model, there is a thin liquid layer between the solid and gas, with combustion occurring in both the liquid and gas phases. Our analysis exploits the largeness of activation energies to derive flame sheet models analogous to those derived for strictly gaseous and strictly condensed deflagrations. For the special case of steady, planar burning, we obtain expressions for the regression rate eigenvalue as a function of the various parameters in the problem. However, a linear stability analysis of this basic solution shows that, for sufficientlylarge values of a certain grouping of parameters, it is unstable to small perturbations which correspond to pulsating, cellular modes of burning.
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