Enhancing combustion performance of Al-H₂O gelled propellants via polytetrafluoroethylene

Aluminum-water (Al-H2O) propellants are a novel class of solid propellants characterized by low cost and low signature observability. However, the inherently high aluminum content in these formulations often leads to severe agglomeration of aluminum (Al) particles during combustion, which in turn compromises combustion efficiency and results in substantial solid residue. Fluoropolymers such as polytetrafluoroethylene (PTFE) have recently attracted attention as effective additives that can chemically interact with the oxide shell on aluminum particles, thereby mitigating agglomeration and enhancing both the combustion and injection performance of Al-H2O systems. In this study, fluoropolymer materials were incorporated into Al-H2O hydrogel propellants for the first time via a surface-coating strategy. Thermogravimetric, laser ignition, and SRM tests show that PTFE addition reduces Al agglomeration and improves combustion efficiency. At 4.5 wt%, CCP size drops from 685 μm to 526 μm, and efficiency increases from 78.52% to 94.02%. Excessive PTFE (7.5%) leads to larger CCPs and reduced efficiency. PTFE also raises the burning rate to 3.48 mm/s and boosts injection efficiency from 21.43% to 51.67%. A dynamic agglomeration model shows that PTFE enhances combustion by increasing aerodynamic forces, weakening liquid bridges, thinning the melt layer, and generating more gas. These findings guide Al-H2O propellant optimization.