A facility for solid-propellant response measurements under pressure-driven conditions

Abstract

An acoustic driver system was developed to investigate unsteady combustion characteristics of solid propellants under pressure oscillations. Two model airplane engines driven by an electric motor were used to produce nearly sinusoidal pressure variations; a consistent peak-to-peak pressure variation of 10% of the mean pressure was obtained using the engines. A pressure insensitive, sub-miniature load cell was used to measure the thrust response of the solid propellants. The load cell was placed in a ceramic holder to protect it from the high temperature of gaseous products evolved during experiments, and the bottom of the holder was coated with several layers of a damping material to reduce the effect of vibrations produced by the engines. Measurements of the thrust response were successfully made over the frequency range 4-130 Hz near atmospheric pressure in air. A minimum signal-to-noise ratio of 3:1 was obtained using the system, and both amplitude and phase information could be simultaneously extracted from the thrust response data. The reliability of the present acoustic driver system was verified by comparing response data obtained from the present and radiation-driven facilities under radiation-driven conditions. For an AP/HTPB composite propellant under pressure-driven conditions with the present facility, maximum non-dimensional thrust responses at 35 W cm-2 were measured at 12 and 16 Hz, respectively, where the phase passed through approximately zero.