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The deflagration of confined porous energetic materials is generally accompanied by an increasing pressure difference, or overpressure, between the burned gaseous products outside the porous solid and the unburned reactants deep within the pores of the material. Although for sufficiently small overpressures the overall structure of the combustion wave possesses a gaseous preheat region between the material surface and the gaseous reaction zone, at higher overpressures and/or sufficiently large surface reaction rates, there is a tendency for the surface temperature to approach the burned-gas temperature, causing the gaseous preheat region to disappear and the reaction zone to lie in the vicinity of the material surface. In this burning regime, there is a single merged reaction-zone structure in which both solid-surface and distributed gas-phase reactions occur. A large-activation-energy analysis of this wave structure is presented, complementing a previous study of the present model that assumed a positive standoff distance between the gaseous reaction zone and the solid material. An expression for the burning rate is derived, showing the expected transition from weak to strong pressure sensitivity in the burning-rate response as the over-pressure increases and convective preheating of the material begins to play a greater role. A fit of this burning-rate formula to relevant data for cyclotetramethylenetetranitramine C 4 H 8 N 8 O 8 , at less than 100% theoretical maximum density indicates reasonably good agreement with experimental results. |
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