ADDITIVES TO REDUCE COKING IN ENDOTHERMIC FUEL HEAT EXCHANGERS

Aircraft designed for hypersonic flight use fuel to cool the ramjet/scramjet propulsion system. Sensible heating and endothermic reactions are used to provide cooling and may produce fuel temperatures that exceed 1200 degrees F. At these temperatures carbonaceous deposits (coke) form. These deposits can inhibit fuel flow, reduce heat transfer, and create hot spots. Coke deposits are known to form by three different mechanisms: 1) An oxidative mechanism involving dissolved oxygen, 2) a reaction between the fuel and metals in the flow path walls that produces carbon filaments, and 3) A gas phase mechanism in which high molecular weight hydrocarbons are formed from the products of thermal cracking reactions (condensation mechanism). Although methods are currently available for controlling the first two coke formation pathways, a means to control the third mechanism is needed.Thus, the objective of the proposed work is to identiy compounds that can be added to the fuel to inhibit the coke formed by the condensation mechanism. In Phase I, TDA will add candidate suppressants to fuel and measure their effect on coke deposition rates.