Response function measurement using an ultrasonic technique in an oscillatory burner

In order to study transient phenomena, an oscillatory burner was designed to create pressure oscillations by means of a rotary nozzle. Using an ultrasonic echolocation technique, the dynamic burning rate of a solid propellant can be measured in real time and compared to the pressure trace. One may extract the response function, and consequently, the dynamic behavior of the propellant from this information. We intend to conduct an empirical study to discern the effect of propellant composition on response function. Our ultrasonic system is designed to operate at pressures up to 20.7 MPa (3000 psi). The ultrasonic transducer sends a high frequency pulse (2.25 MHz for our experiments) through the bottom of the propellant to capture the surface as it burns. Two piezoelectric pressure transducers record the pressuretime history during each experiment. We use an inert gas (helium) feed to pre-pressurize our chamber, and allow us to vary the operating pressure. Control of the mean pressure and pressure amplitude of the oscillations is achieved by varying the sizes of steady state and oscillatory exhaust nozzles. In this study, we run trials at three frequencies (50, 100, and 300 Hz) for each propellant at 300 psi. Data taken for propellants with different binders, additives, and particle size is compared with the baseline propellant to determine the effects of these additives on the response function.