Nonlinear Stability Testing of Full-Scale Tactical Motors

Abstract

The U.S. Naval Air Warfare Center has participated in a program to develop an improved understanding of linear and nonlinear combustion instability in solid propellant rocket motors. One goal of this program was to develop a systematic database of motor stability data. This paper describes the nonlinear aspects of the motor e rings and analysis. The motors used had diameters of 127 mm and were 1.7 m long. The majority were loaded with an 88% solids reduced-smoke ammonium perchlorate propellant with a nominal burning rate of 6.1 mm/s at 6.9 MPa. Motor pressures ranged from 3.45 to 10.34 MPa and various grain geometries were tested. In addition, motors have been e red that contain 1% 8- mm aluminum oxide, 90- mm aluminum oxide, and 3- mm zirconium carbide as stability additives in place of 1% ammonium perchlorate. This paper discusses experimental methods of motor pulsing and various theoretical approaches to predict pulse amplitudes in motors. The paper also examines nonlinear acoustic motor response to various amplitudes of acoustic pulsing and the resultant characteristics of sustained nonlinear oscillations. Finally, some theoretical interpretations are presented from the experimental motor data. The results show that there is a direct relationship between the dc pressure shift and the magnitude of the acoustic oscillations.