Supersonic spray combustion subject to scramjets: Progress and challenges

Supersonic spray combustion is one of the most significant physiochemical processes that occurs in the scramjet propulsion system, and related research can motivate the development of scramjet engines. This paper reviews the research on supersonic spray combustion that has been conducted in the past few decades and focuses on the key physiochemical processes and associated fluid physical mechanisms. Supersonic spray combustion involves not only the typical processes during the combustion of liquid fuel, such as atomization, dispersion, evaporation, mixing and ignition, but also complicated interactions among the spray, turbulence, shock waves and chemical reactions in supersonic flows. The interactions commonly affect the combustion performance in terms of ignition, stability and efficiency. The present work outlines the current research status for spray combustion in subsonic flows. Then a brief description of the basic features of supersonic flow and combustion is provided. For the supersonic combustor in the scramjet engine, the research results and challenges regarding supersonic flow and spray in mixing layers and jets are discussed. The stabilization of supersonic spray combustion and the control methods are introduced and summarized. An outline of the effects of shock waves on combustion, and the shock-induced deflagration and detonation is provided as an overview of the research and development progress since shock waves typically occur in supersonic combustors. Finally, the potential challenges and issues that are encountered in the fundamental research, including numerical models and approaches and experimental techniques and databases, and the applications of supersonic spray combustion are highlighted.