Novel burning rate measurement technique for solid propellant by means of ultrasonics

A novel burning rate measurement technique for solid propellants using ultrasonics has been developed. Ultrasound is applied to the burning surface of the end-burning propellant grain from the bulk side, and the reflected wave, which is frequency-shifted by the Doppler effect, is analyzed with a wavelet technique. This method enables us to get the instantaneous linear burning rate and, thus, can be a strong tool for the instability study of solid propellants. The wavelet method is also favorable for the identification of the reflected signal from the burning surface even if the signal intensity becomes very low and indistinguishable from white noise with normal measuring techniques. Efforts have also been paid to eliminate the coupling material between the ultrasonic probe and the propellant grain to simulate the real situation of rocket motors. An oscillation deadener circuit has been successfully employed to reduce strong multi-deflection signals within a metallic plate between the probe and the propellant grain. With these two improvements, it becomes possible to detect and process the signals in longer propellant grains in the actual solid rocket motor situations.