Particulate Damping of Oscillatory Combustion

An experiment is described in which the attenuation of oscillatory burning by aluminum is studied by means of a self-excited, one-dimensional oscillatory burner. Values of the response function of the combustion zone are presented for several variations of a composite pro pell an I, which differ only in that some contain small amounts of aluminum. The data show that the addition of a small amount of aluminum to the propellant tested has little or no effect upon the response function of the flame (as defined by the Hart-McClure theory). These data show also that, for this experimental system, there is an increased acoustic damping that is caused by the presence of aluminum in the propellant. If this increased damping is ascribed to the formation of condensed A^Os droplets in the combustion gas, it is shown that the theory of Epstein and Carhart can explain the increased damping. As a function of frequency, tjie variables tested in the experimental program were three different aluminum additives, four concentrations of alumina, alumina as an additive, and the effect of pressure.