Combustion characteristics of AP/Al/HTPB fuel droplets with embedded silver wire

Solid propellant embedded with metal wire is a key method for enhancing the thrust of solid rocket motor (SRM). The microscopic reaction mechanisms between the metal wire and the hydroxyl-terminated polybutadiene (HTPB) droplet fuel were studied. Experimental studies were carried out to explore how silver wire influences the combustion behavior of pure HTPB droplets, as well as HTPB droplets blended with ammonium perchlorate (AP) or aluminum powder. Thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) showed that silver wire catalyzes the decomposition of AP in HTPB droplets. The research findings also revealed the characteristic combustion process of HTPB droplets, where the droplet diameter initially increases and then decreases during combustion. The embedding of metal wires individually increased the high-temperature region within both pure HTPB droplets and HTPB droplets containing AP and aluminum powder, thus accelerating the combustion rate. For pure HTPB droplets, the rate increased from 2.59 mm² s⁻¹ to 2.81 mm² s⁻¹, while for the HTPB droplets with AP and aluminum powder, the rate increased from 2.63 mm² s⁻¹ to 3.41 mm² s⁻¹. Silver wire similarly accelerates the combustion rate of this composite system, exhibiting a stronger catalytic effect on AP decomposition. This is attributed to the silver oxide generated by heating the silver wire, which catalyzes the decomposition of chlorate ions within AP. Furthermore, a theoretical model combining metal wire heat conduction with HTPB pyrolysis was developed, highlighting the impact of the metal wire on internal heat transfer and its contribution to enhancing the combustion rate. This study offers a theoretical basis for optimizing the design of metal-embedded propellants.