Endothermic fuels for hypersonic vehicles

The use of hydrocarbon fuels for hypersonic vehicles will require increasing utilization of the fuel as vehicle speed increases. In order to achieve maximum heat sinks endothermic reactions must be employed to augment fuel enthalpy. Various reactions, such as thermal cracking, depolymerization, dehydrogenation, and dehydrocyclization, can be used and have been studied. Of these, the catalytic dehydrogenation of naphthenes shows the most promise for practical application. The dehydrogenation of MCH over a Pt/AJfoOa catalyst can approximately double the 1000 Btu/lb available from fuel enthalpy. This should provide cooling sufficient to allow flight into the range of Mach 10 at optimum altitude. However, the application of cooling to the various portions of the aircraft will present formidable problems. Factors that are important in this consideration such as thermal stability, reaction rate, reactor weight and volume, heat transfer, pressure drop, combustion characteristics, and the mating of the cooling system to the aircraft are discussed.