A review of cooling technologies for scramjet engines and the mechanisms of fuel heat absorption and coking in cooling channels

The thermal barrier problem encountered in hypersonic vehicle engines has emerged as a critical bottleneck that directly constrains flight safety, and its effective mitigation remains an urgent challenge. Although regenerative cooling (RC) technologies that employ fuel as the coolant can substantially reduce the thermal load of the engine, their long-term efficiency remains constrained by coke deposition within cooling channels. Consequently, optimizing cooling technologies, enhancing fuel heat sink performance, and suppressing coking have become research priorities in addressing the safety and performance requirements for hypersonic flight. This paper offers a comprehensive review of recent developments in thermal management systems for hypersonic propulsion. First, key cooling technologies in hypersonic propulsion systems are summarized, with particular emphasis on research advances in the most promising RC systems. Secondly, the influence of fuel molecular structures on heat sink performance was analyzed, and recent findings in high-density endothermic hydrocarbon fuels (HDEHFs) for hypersonic applications were reviewed. Finally, based on the framework of radical chain reaction theory, this review highlights the coking mechanism and suppression strategies for hydrocarbon fuels under supercritical conditions. Overall, this review aims to provide theoretical underpinnings and research directions for the comprehensive treatment of hydrocarbon fuel coking issues within the cooling systems of hypersonic vehicles.