Heterogeneous effects on dynamic burning in composite solid propellants

Two transient heterogeneous propellant combustion models, applicable to fine oxidizer composite, propellants, are examined. The models differ in the mechanism by which mass conservation at the surface is maintained. The surface accumulation model supposes that components accumulate in a layer at the surface. Each component reaches an equilibrium concentration inversely proportional to its burning rate. The double reaction layer model supposes that a molten binder layer covers the propellant. The oxidizer gasifies underneath the layer, while the binder gasifies at the surface. Both models are perturbed to calculate a burning-rate response function. The results are compared to recently published burning-rate response function measurements made using laser recoil. The double reaction layer model qualitatively produces features observed in the experimental data: a sharp resonance peak accompanied by a shift from negative to positive phase. The surface accumulation model does not produce these features. The presence of time delay terms - the time lag is caused by heat conduction through the binder layer - in the double reaction layer model accounts for the sharp resonance peak. The frequency of the peak produced by the model is lower than what is observed in the data; this discrepancy is attributed to uncertainties ill the properties of the binder layer.