The extent to which the benefits of hydrocarbon fuel cooling technology can be realized depends on our ability to manage coke deposits. The coke deposits, which may form in heat exchangers, reactors and on inside surfaces of fuel system components, degrade heat transfer, catalyst activity, and fuel flow characteristics and can lead to system failure. Therefore, in situ regeneration of fouled surfaces was investigated as a practical approach for reducing the impact of coke formation on aircraft thermal management systems.
Thermogravimetric analysis (TGA) was used to evaluate various surface regeneration techniques (such as carbon burnoff in air or oxygen and carbon gasification using CO2 or steam) and to compile a database for kinetics analysis. The most practical technique for in situ surface regeneration of heat exchangers and reactors is the carbon burnoff method. Although the burnoff method is simple and cost-effective, care must be taken to control strong exothermic reactions. For this reason, a kinetics model and a computer simulation have been developed to guide the selection of the key operating variables (i.e., temperature, pressure, and time) for the in situ regeneration method. A surface regeneration simulator was constructed and used to assess the effectiveness of the in situ regeneration techniques and validate the kinetics model. Use of the computer simulation tool in a real application to specify the conditions for removing coke deposits from a fouled heat-exchanger/reactor panel from a scramjet test engine is discussed in the paper.