Enhancing combustion and injection performance of aluminum-water gelled propellants via bismuth oxide

Aluminum-water (Al-H₂O) propellant is a promising class of environmentally friendly propellants with the potential to reduce harmful emissions associated with conventional solid propellants, thereby mitigating environmental pollution. However, current formulations of Al-H₂O propellants generate substantial solid residues upon combustion, which can reduce specific impulse and pose a risk of nozzle blockage. To enhance the combustion and injection behavior of Al-H₂O propellants, this work presents a novel approach that modifies aluminum powder with bismuth oxide (Bi₂O₃), harnessing their intrinsic chemical interaction. Thermogravimetric analysis and laser ignition experiments demonstrate that the incorporation of Bi₂O₃ improves the injection efficiency of Al-H₂O gelled propellants while reducing the formation of solid combustion residues. This enhancement is attributed to the reaction between Bi₂O₃ and aluminum, which increases the production of gaseous combustion products. In addition to its catalytic effect, Bi₂O₃ significantly mitigates aluminum agglomeration during combustion, contributing to improved combustion efficiency in Al-H₂O gelled propellants. The incorporation of 10 wt% Bi₂O₃ notably boosted injection efficiency from 27.95 % to 54.76 %, while combustion efficiency increased from 80.15 % to 89.56 %. Hot firing of rocket motor tests further demonstrated that the incorporation of 10 wt% Bi₂O₃ led to an increase in specific impulse from 1270 N·s/kg to 2001 N·s/kg, highlighting the significant enhancement in propulsion performance. The findings of this study provide valuable insights into the performance optimization of Al-H₂O gelled propellants, offering a new perspective on their formulation and application.