Nitramine Smokeless Propellant Research.

A transient ballistics and combustion model is derived to represent the closed vessel experiment that is widely used to characterize propellants. The model incorporates the nitramine combustion mechanisms which are contained within the steady-state model developed as a part of last years FY 1976 research. A computer program is developed to solve the time-dependent equations, and is applied to explain aspects of closed vessel behavior. It is found that the rate of pressurization in the closed vessel is insufficient at pressures of interest to augment the burning rate by time-dependent processes. In the case of nitramine propellants, however, the cratering of the burning surface associated with combustion above break-point pressures augments the effective burning rate as deduced from the closed vessel experiment. Low pressure combustion is significantly affected by the ignition process and, in the case of nitramine propellants, by the developing and changing surface structure. Thus, burning rates deduced from the closed vessel experiment may of may not agree with those measured in the equilibrium strand burner. Application of the model to closed vessel test cases shows good agreement between theory and experiment. Series of T-burner experiments are performed to compare the combustion instability characteristics of nitramine HMX-containing propellants and ammonium perchlorate AP propellants. It is found that the inclusion of HMX consistently renders the propellant more stable. Although ash produced by more fuel-rich propellants could have provided mechanical suppression, results from clean-burning propellants permit the conclusion the HMX reduces the acoustic driving.