Acoustic amplification during solid propellant combustion

The oscillatory combustion behavior of unmetallized solid propellants burning in a T-burner has been interpreted through phenomenological considerations of how solid propellant flames act as a source of amplification for acoustic pressure waves. The data show the expected variation of the specific amplification with the frequency of oscillation, but also show an additional important effect of mean chamber pressure. This latter observation is not predicted by any of the past transient burning analyses for combustion instability. The results of the T-burner tests have been incorporated into a realistic correlation for the rating of propellants to determine the range of frequency and pressures where amplification of acoustic waves is possible. It is observed that on a map of chamber pressure (burning rate) versus frequency, lines of constant specific amplification form loops, and that these contours show a locus of pressures as a function of frequency where amplification is maximum.