Combustion Characteristics and Ballistic Performance of Dual-Layer Propellant Grains for End-Burning Type Rocket Motors

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A laboratory-scale rocket motor of the end-burning type has been used to characterize the combustion aspect and ballistic performance of concentric dual-layer propellant grains. The inner-layer and the outer-layer are polybutadiene∿potassium perchlorate-based propellant with comparatively high regression rate and slow burning polyurethane∿ammonium perchlorate propellant, respectively. Under the condition of constant outer-layer diameter firing experiments have been carried out varying the inner-layer diameter et al., in order to determine optimum grain design. Increasing the ratio of the inner-layer to the outer-layer diameter resulted in remarkable increase in the steepness of pressure-time curves. It was noted that there occurred a gutter in the boundary region of these two grain layers at the burning surface where the steady-state combustion was interrupted. An erosive burning effect due to the interaction of turbulent gas flows generating from each burning surface with different regression rates, was postulated as the most likely cause of this phenomenon. By means of one-dimentional transparent midget motor, characteristics of heterogeneous combustion of dual-layer grains containing Al and Al-Mg alloy particles, were discussed and compared with those of simple end-burning grain.
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