Initiators for Endothermic Fuels

Aircraft designed for hypersonic e ight must incorporate active cooling in the propulsion system. Hydrocarbon cracking reactions produce a high endotherm; however, without a catalyst these reactions require very high temperatures, which reduces the allowable stress in the heat exchanger materials and increases wall thickness and weight.Thegoalofthisinvestigationwastodetermineifchemicalinitiatorscouldacceleratetherateofhydrocarbon crackingreactionsandreducetherequiredtemperaturesinahypersonicaircraftheatexchanger/reactor.Wemixed numerousinitiatorswith n-heptaneand measuredtherateof cracking.Thesetestswereconductedattemperatures of 450, 500, and 550 ±C, and at a pressure of 37 atm. We identie ed several chemicals that produced substantial increases in measured cracking rates when added to the fuel at concentrations from 0.5 to 2.0 wt%. The best initiator is soluble in the fuel, stable in its concentrated form, and is not highly toxic.