Inert Particles for Axial-Combustion-Instability Suppression in a Solid Rocket Motor

Various factors and trends related to the presence of inert particles in the central core flow as a means to suppress axial-combustion-instability symptom development are numerically predicted for a composite-propellant cylindrical-grain motor. Individual transient internal-ballistic-simulation runs show the evolution of the axial pre sure wave and associated base pressure shift for a given inert particle size and loading percentage, as initiated by a given pressure disturbance. The pressure wave's limit magnitude at a later reference time in a given firing simulation run is collected for a series of runs at different particle sizes and loadings and is mapped onto an attenuation trend chart in a format potentially useful for motor designers evaluating their specific motor design and particle loading requirements (and, in turn, allowing for less experimental test firings, if the numerical results are relatively accurate). When the effect of acceleration (through structural vibration of the propellant surface) on the combustion process is included in the numerical calculations, one observes substantial differences in burning and internal How behavior in the presence of axial-pressure-wave activity, as reflected in individual firing simulations and the corresponding particle attenuation map. The predicted base pressure shift is more pronounced at lower particle loadings: for example, in conjunction with the pressure-wave magnitude being larger, when the propellant's burning process is substantially sensitive to normal acceleration. Whether the propellant's burning rate is acceleration-sensitive or not, the inert particles' presence in the central core flow is demonstrated to be an effective means of suppression, correlating with past experimental successes in the usage of particles. Particle/burning-surface interactions, which may also act to suppress pressure-wave development by changing the propellant's inherent frequency-dependent combustion response, are not explicitly accounted for in this study, although one or two of the combustion-response model's pertinent coefficients could be altered to reflect this change, given sufficient information in this regard.