Nonlinear axial combustion instability in solid propellant motors
Nonlinear axial combustion instability occurs when one or more strong gaseous compression waves propagate longitudinally within a solid piopellant rocket motor The nonlinear unsteady flow field deiives energy through interaction with the combustion process and causes an inciease in the time-aveiaged buining late, pressuie, and tluust This behavior has been investigated using polyui ethane-ammonium perchloiate piopellants and some 200 motois in the size lange 2-in -diam X 10-in -long to 17-in -diam X 180-in -long Reproducible i esults weie obtained The motois weie found to be linearly stable and nonlineaily unstable with respect to initiation of instability Ihus, normal proof firings aie unlikely to detect inheient instability, since a flow distuibance of finite amplitude is required to trigger the system A pulse injection method of triggeiing was applied to all firings As operating piessmes incieased above a critical value P s* the motois became capable of instability, the seveiity increasing monotonically with the i estriction ratio The effect on P * of changing the motor scale, length to diametei ratio, grain cross section, giain temperature, and of adding aluminum alloy and lithium fluoride to the propellaiit was deteimined