Evaluation of the gas-phase thermal decomposition behavior of future jet fuels

Thermal stability is of particular concern for future hypersonic jet fuels due to prolonged exposure, the need for heat dissipation, and the possible formation of undesirable deposits at elevated temperatures. The gas-phase thermal decomposition of four jet fuel candidates (methylcyclohexane, toluene, trans-decalin, and naphthalene) has been measured under precisely controlled conditions of reaction atmosphere, exposure temperature, and residence time. Differences in fuel thermal decomposition were analyzed with respect to molecular structure and thermochemical bond energy analysis. The thermal decomposition data for these compounds have also been used to evaluate their potential heat-sink capacities. In a separate but related study, the gas-phase thermal degradation behavior of trans-decalin was examined for a broad range of reaction conditions. The results indicate that removal of oxygen from the fuel-handling system and a reduction in high-temperature exposure time will greatly enhance the fuel's gas-phase stability. The formation of degradation products was found to be most dependent on the composition of the flowing gaseous atmosphere. Under pyrolytic reaction conditions, the nature of trans-decalin reaction products was consistent with an initial degradation pathway involving C-H bond homolysis followed by H atom abstraction reactions.