RESEARCH PROGRESS ON HIGH-MACH-NUMBER SCRAMJET ENGINE TECHNOLOGIES

Hypersonic airbreathing flights are highly valued in both the fields of space transportation and national aerospace safety, and the scramjet engines are pivotal propulsion devices for these flights. The scramjet engines for flight Mach numbers within the range between 4.0 and 7.0 have been extensively studied and well developed in recent years, and the extension to the scramjet engines for higher flight Mach numbers within the range between 8.0 and 10.0 or even higher are sure to be a competing focus for near-space competitions in the following decades. The current paper analyzes and summarizes the recent research advances of scramjet engines with flight Mach numbers within the range between 8.0 and 10.0+ . First of all, the key scientific problems and technologies of the higher Mach number scramjet engines are highlighted, including the high-temperature dissociation and thermochemical nonequilibrium effects, mixing and combustion enhancement technologies in ultra-high-speed flows, the matching of hypersonic combustion and inflow compression and the operating modes, the high-enthalpy low Reynolds number boundary-layer flows and the boundary-layer flow control methods, the thermal protection technologies of high-enthalpy low-density combustion inflows, and the ground test facility technologies for high-Mach number scramjet engines, respectively. Second, the experimental apparatus related to high-enthalpy shock tunnels and the shock tunnel driving technologies and typical ground and flight experiments of the high-Mach number scramjet engines home and aboard in recent years are introduced. Third, research advances including overall performance analyses of thrusts and thermal protections, the prominent high-enthalpy dissociation and thermochemical nonequilibrium effects in high-Mach-number scramjet engines, and mixing and combustion enhancement technologies in the ultra-high-speed flows are reviewed, so as to assess the feasibilities of high-Mach-number scramjet engines, and to discuss the features of engines’ key technologies. Finally, the summary is presented and several suggestions are proposed for further studies of the higher Mach number scramjet engines.