Abstract: Boron-loaded gel fuel is an ideal propellant to power limited-volume propulsion devices such as ramjet, but its high viscosity and complex rheological properties bring significant challenges for practical application. Taking a novel gel fuel with boron content of 50 wt.% as the research object, a series of experiments were designed considering the complex environment potentially encountered in engineering applications to explore the influence of change rate of shear rate, constant shear duration, pre-shearing, temperature and other factors on the viscosity of boron-loaded gel fuel, and the experimental phenomena were thoroughly analyzed based on shear stress. The results indicate that a power function with constant term can accurately describes the time-dependent viscosity of the gel fuel under constant shear rate. Pre-shearing treatment can effectively destroy the structure of boron-loaded gel system, leading to limited recovery within a short period, while high-low temperature cycling has minimal destructive effect on the gel structure but reduces its overall structural strength. Furthermore, there is a critical temperature at a constant shear rate: below this temperature, the viscosity of the gel fuel exhibits a positive correlation with temperature; above it, the viscosity has no significant change. The analy-sis based on shear stress shows that the boron containing gel system used in the study has a multi-level structure, and the secondary structure recovery ability is stronger than the advanced structure when subjected to high-low temperature cycling. Based on the shear stress analysis, it can be inferred that the boron-loaded gel system used in the research has a multi-level structure. When subjected to temperature cycling, the secondary structure has a stronger recovery ability than the main structure.

Key words: boron-loaded gel fuel, non-Newtonian fluid, rheological properties, viscosity, air breathing engine