Preferred frequency oscillatory combustion of solid propellants

Two systems were used for the study of low-frequency oscillatory combustion. The first was a small end-vented burner that employed end-burning grains and produced nonacoustic pressure oscillations. The second system was a side-vented, double-end burner of suitable lengths to produce low-frequency (5 to 320 cps) acoustic pressure oscillations. The propellant tested most extensively (a metallized double base) exhibited oscillations only over a very restricted pressure-frequency region. This region was similar for each type of burner. From these results it was inferred that the response function of the combustion zone showed a marked peak when plotted as a function of frequency at low pressures. Similar behavior was shown by a highly aluminized composite propellant; however, other propellants did not reveal the phenomenon.