Review on synthesis and properties of high-energy-density liquid fuels: Hydrocarbons, nanofluids and energetic ionic liquids

High-energy-density (HED) liquid fuels are critical for volume-limited aerospace vehicles to extend the flight range and increase the payload, and can be used as an energetic additive for conventional fuels. This review will summarize the synthesis and properties of HED fuels along with challenges appearing especially in the past decade. The currently used multi-cyclic HED fuels are introduced first with a focus on more efficient and greener synthesis routes. Then the synthesis of new multi-cyclic, strained and caged fuels with higher energy is summarized, mainly including the reaction mechanism and catalysts involved. After that, HED biofuels synthesized from biomass feedstock including terpene, hemicellulose, cellulose and lignin are comprehensively reviewed. Nanofluid HED fuels are further introduced as an alternative way to increase the energy density of liquid fuels by adding energetic nanoparticles. Hypergolic energetic ionic liquids are then summarized as a special alternative for toxic and hazardous hydrazine. Finally we will emphasize the problems need to be resolved in the synthesis and application of HED fuels. This review article will be helpful to explore and develop better approach and process for HED-fuel synthesis and upgrade for advanced propulsion applications. This work has been selected by the Editors as a Featured Cover Article for this issue.