Additives to Prevent Filamentous Coke Formation in Endothermic Heat Exchangers

摘要

Aircraft that travel at hypersonic speeds must use fuel to cool the ramjet/scramjet propulsion system. Both sensible heating and endothermic reactions can be used to provide the required heat sink; however, in the process the fuel temperature can reach 650 deg C (1200 deg F). When fuel reaches these temperatures, carbonaceous deposits (coke) form on the walls of the heat exchangers. These deposits can inhibit fuel flow and reduce transfer across the heat exchanger surface. Coke foramtion is a complicated process and deposits are known to form by at least three different mechanisms: an oxidative mechanism involving dissolved oxygen in the fuel (1,2) a gas phase mechanism in which high molecula weight hydrocarbons are formed from the products of thermal cracking reactions (condendation mechanism) (3,4,5,6), and finally a reaction between the fuel and metals in the flow path walls, which produces carbon filaments (7,8,9). Although methods currently are avaiable for controlling the oxidative and condensation pathways (1,2,5,10), a practical means to control the filamentous mechanism, which is the dominant coke formation mechanism under these conditions, has not yet been identified.