The combustion process of gun propellants packed in high loading density conditions can differ significantly from those burning individually in the same pressure and temperature environment. More specifically, burn rates and flame spreading processes for a propellant charge are not only functions of pressure and initial temperature, but also a function of the loading density (or gap width between adjacent propellants). This experimental study has been conducted to investigate the influence of gap space between propellants on propellant regression rates. In the experimental setup, two opposing strands of JA2 gun propellant were burned in a double-ended windowed strand burner (DEWSB). The DEWSB consists of two identical propellant feeding systems adjoined to a center combustion chamber. To measure the gap width between the two strands, a contrasting image between the propellant strands and the background was used. To obtain a constant gap width between the opposing propellants, an image was imported into a LabVIEW control feedback loop. A series of tests was conducted for a pressure range from 0.69 to 3.45 MPa, and a gap distance range from 2 to 12 mm. Comparing regression rate data of JA2 propellant burned in the double-end configuration to that of a single strand, an increase in the regression rate of about 30% was observed for the pressure range tested. This increase occurs for a certain gap width range, which was found to be a function of pressure. The enhancement of the burn rate is caused by the geometric confinement of the flame, which applies a greater energy feedback to the burning propellant surface.

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