Initiators for endothermic fuels

Aircraft designed for hypersonic flight must incorporate active cooling in the propulsion system. Hydrocarbon cracking reactions produce a high endoth erm; however, without a catalyst these reactions require very high temperat ures, which reduces the allowable stress in the heat exchanger materials an d increases wall thickness and weight. The goal of this investigation was t o determine if chemical initiators could accelerate the rate of hydrocarbon cracking reactions and reduce the required temperatures in a hypersonic ai rcraft heat exchanger/reactor. We mixed numerous initiators with n-heptane and measured the rate of cracking. These tests were conducted at temperatur es of 450, 500, and 550 degreesC, and at a pressure of 37 atm. We identifie d several chemicals that produced substantial increases in measured crackin g rates when added to the fuel at concentrations from 0.5 to 2.0 wt%. The b est initiator is soluble in the fuel, stable in its concentrated form, and is not highly toxic.