International Journal of Energetic Materials and Chemical Propulsion

TEMPERATURE SENSITIVITY MEASUREMENTS AND REGRESSION BEHAVIOR OF A FAMILY OF BORON-BASED VERY HIGH BURNING RATE PROPELLANTS

RÉSUMÉ

The combustion behaviors of three formulations of very high burning rate (VHBR) propellants are being studied. These formulations contain 0, 2, and 4% boron hydride, B₁₀H₁₀, the burning rate catalyst. Two diagnostic tools were used in this study: a realtime X-ray radiography (RTR) system with a high-pressure double-windowed (HPDW) test rig and a pressure and temperature controlled optical strand burner (OSB). The RTR system is used to obtain instantaneous X-ray images of the solid propellant grain as it burns during a transient test at pressure up to 340 MPa (50,000 psi). The optical strand burner maintains a steady pressure up to 41.4 MPa (6,000 psi) and allows the initial temperature of the strand to be set from −40°C to +70°C (−40°F to + 158°F).
For a typical RTR test using the HPDW test rig, the instantaneous, internal burning surface of a center-perforated grain was observed. The results show that the grain remained as a consolidated piece even at a high regression rate of 200 cm/s. From these images, instantaneous burning rates were deduced for all three formulations. These burning rates were compared with earlier results obtained by the authors from end-burning grains under similar transient conditions. These two sets of burning rates are in reasonable agreement.
The OSB was used to study the temperature sensitivity (σ_p) of VHBR propellants. Determining propellants' temperature sensitivities as functions of pressure and temperature is important in the study of transient burning phenomena. It was found that σ_p increases as initial temperature (T_i) decreases. As a result of a slope break in the burning rate, σ_p exhibits discontinuities as functions of pressure and T_i.
From a recovered sample which was extinguished at 331 MPa (48,000 psi), the burning surface was found to be non-smooth and covered with a melt layer containing many small indentations.