Experimental apparatus showing the motor with the pressure-modulation apparatus above and the ultrasonic transducer connected below. The transducers monitoring chamber pressure can be seen attached to the motor midsection. The motor exhausts upward.
Propellant sample ready for testing. A layer of epoxy is cast around the sample to prevent lateral burning.
Schematic of the major system components.
Correspondence between the sample geometry and the pulse-echo ultrasonic wavelet. From left to right, the first set of wavelets (1) is the signal from the transducer. The second set (2) is the echo from the back of the transducer. The third set (3) is the echo from the coupling/sample interface. The fourth set (4) is the echo from the sample surface. The purpose of the coupling material is to protect the transducer from the hot, corrosive gases and delay the return of the propellant surface echo (4) so that it can be discerned from the input wavelet (1).
Cross section of the vented combustion vessel with attached propellant sample holder, ultrasonic transducer, and fluidic valve.
Pretest (a) and post-test (b) calibration data showing the echo time for the propellant/coupling assembly and the echo time for the coupling material alone as a function of pressure.
Example output voltages from all transducers during the 17 Hz (a) and 70 Hz (b) experiments.
Chamber pressure for the 17 Hz (top) and 70 Hz (bottom) experiments.
Detrended ultrasonic signal for the 17 Hz (top) and 70 Hz (bottom) experiments. Superimposed in gray are the low pass filtered signals.
Burn rates for the 17 Hz (top) and 70 Hz (bottom) experiments.
Propellant formulations and physical characteristics
Summary of input and output data from the example tests.
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