Pulse Triggered CI In SRMs: A Comprehensive Review of Nitramine, Aluminum and AP Particle Size

Pulse triggered combustion instability in solid rocket motors (SRMs) arises from nonlinear coupling between unsteady heat release and chamber acoustics when a finite amplitude perturbation, such as a pressure pulse, drives the system beyond its stability threshold. Over the past several decades, theoretical, numerical, and experimental studies have shown that triggering behaviour depends not only on chamber geometry and operating conditions but also on the detailed combustion response of the propellant, which is strongly influenced by nitramine content, aluminium loading, and ammonium perchlorate (AP) particle size. Nitramine oxidizers (RDX, HMX) modify burning rate, pressure exponent, and transient response, often increasing the pressure coupled gain, while aluminium particles introduce two phase effects that can either damp or drive instability depending on loading and agglomeration behaviour. AP particle size controls flame structure, burning rate, and low frequency coupling, thereby shaping the overall stability landscape. This review synthesizes key developments in pulse triggered instability theory, experimental methodologies for pulsed testing, and the documented influences of nitramine content, aluminium content, and AP particle size on combustion stability, with emphasis on their integrated impact on pulse triggered behaviour in SRMs.