Mechanisms and Methods of Suppression of Combustion Instability by Metallic Additives

HE problem of unstable burning has been recognized in solidpropellant rockets since 1941. With the advent of pressuremeasuring systems having adequate frequency response, it was discovered that unstable burningwas associated withpressureoscillations in the motor having frequencies corresponding to acoustical modes of the cavity. In the 1950s, when this work was conducted, much of the work in the investigation of unstable burning was of a “ quick e x” nature; signie cant theoretical analyses were not conducted until late in the decade. Owing to the complex species and conditions that exist in a burning solid propellant, these theories necessarily involved a number of simplie cations and assumptions that experimental results often tended to refute. Therefore, an experimental study was undertaken to investigate possible mechanisms for unstable burning and to determine various means of suppressing the oscillations. Mechanism of Suppression So that studies of suppression may be made, it is necessary to consider the various theories of oscillatory burning and the accompanying reactions. The general theory is that random noise may be amplie ed through some feedback path yielding acoustical waves, in accordance with the possible modes outlined by Lord Rayleigh. It may be shown that suppression of oscillatory burning may result from two sources: 1) attenuating the acoustical wave by absorption, ree ection, or scattering; and 2) altering the feedback path by changing the physical or chemical requirements for reaction. The latter source may be further subdivided by considering the site of the controlling feedback reaction as either the condensed phase or the gas phase. During the course of this study, a mechanism for suppression according to source 1 was proposed by Neustein and Altman, 1 based on the theoretical work of Epstein and Carhart 2 and the experimental e ndings of Zink and Delsasso 3 on the effect of solid particles