Boron-loaded gel fuel is an ideal propellant for limited-volume propulsion devices such as ramjets. However, its high viscosity and complex rheological properties pose significant challenges to its practical application. In this study, a novel gel fuel with 50wt% boron content was used as the research object. Based on the complex service environments in engineering applications, a series of experiments were designed to investigate the effects of shear rate change rate, constant shear duration, pre-shearing, and temperature on the viscosity of boron-loaded gel fuel. The experimental phenomena were analyzed in depth based on shear stress. The results show that under constant shear rate, the time-dependent viscosity of boron-loaded gel fuel can be accurately described by a power function with a constant term. Pre-shearing can effectively destroy the structure of the boron-loaded gel system and make it difficult to recover within a finite time. High-low temperature cycling can hardly destroy the gel structure but can reduce its structural strength. At a constant shear rate, there exists a critical temperature: below this temperature, the viscosity of the gel fuel is negatively correlated with temperature; above this temperature, the viscosity does not change significantly. Based on shear stress analysis, it is inferred that the boron-loaded gel system has a multi-level structure. Under high-low temperature cycling, the recovery ability of the secondary structure is stronger than that of the main structure.

The boron-loaded gel propellant, made by adding boron powder, gelling agents and other modified substances into liquid fuel, is an ideal fuel providing power for limited volume propulsion devices such as ramjets. However, the application of boron-loaded gel propellant also brings new technical challenges such as preparation of high-boron-content gel propellant with excellent stability and rheological properties, controllable supply and efficient atomization of propellant, and efficient combustion organization of ramjets. The development history of boron-loaded gel propellant and related research work are summarized, and the atomization technology of gel propellant is introduced in detail. On the basis of integrating a large number of research achievements, the problems that still need to be further studied are presented. The combustion characteristics of single droplets and spray of boron-loaded gel fuel are summarized, the research work on boron-loaded gel ramjets at home and abroad reviewed, and the combustion organization characteristics of boron-loaded gel ramjets introduced. Finally, the research direction of boron-loaded gel ramjets is summarized.