Review on metal fuels and its application in ramjet engines

Metal fuels, with their high energy density, show significant advantages in improving engine specific impulse and thrust, and have become a frontier in propulsion technology research. This paper reviews the characteristics, fuel forms, and the progress in the application of metal fuels in ramjet engines. The physicochemical characteristics and energy performance of common metal fuels such as lithium, beryllium, boron, magnesium, and aluminum are analyzed. The working mechanisms, performance characteristics, and advantages and disadvantages of the pill-type and powder-type metal fuel forms are compared. This paper focuses on summarizing the application of metal fuels in air ramjet engines, water ramjet engines, and cross-medium engines. The test and numerical simulation results of combustion organization, flow field optimization, and performance enhancement from both domestic and international research are classified and summarized. Furthermore, the current technical challenges are revealed. A summary and outlook on the key technical challenges in the combustion organization of metal fuel engines are presented. This provides reference for future research and engineering applications of metal fuels.