The effect of dissolved oxygen on the pyrolytic degradation of jet fuels

Future high-speed aircraft will require fuels that can withstand high temperatures and pressures. Research into the mechanisms of degradation has revealed that fuels undergo different degradation mechanisms at different temperatures. At relatively low temperatures (150°C–250°C), the fuel reacts with dissolved oxygen in a process termed autoxidation to form gums and varnishes. At higher temperatures (<400°C) pyrolysis takes place, and the fuels break down to form carbonaceous solids. Between these two temperatures, intermediate reactions occur. Although much research has been done on autoxidation and pyrolysis, little research has been done on the intermediate reactions or the link between the two regimes.; This research focuses on the effects of the presence of dissolved oxygen in the fuel. The hypothesis of this work is that the presence of dissolved oxygen in a fuel has an effect on the pyrolytic deposition behavior and thermal stability of the fuel. The effect, namely increasing or decreasing the deposit formation, is dependent on the fuel composition. Six fuels were tested for this work: three fuels consisting largely of hydroaromatic and aromatic compounds, and three fuels consisting mainly of naphthenic compounds. These fuels were expected to be thermally stable.; Removal of dissolved oxygen via nitrogen sparging increased the pyrolytic stability of all six fuels. The process of nitrogen sparging removed volatile compounds from the fuel, which may have increased the thermal stability of the fuels at higher temperatures. The fuels were also rated in thermal stability. Those containing naphthenic compounds were found to be more stable than those containing hydroaromatic and aromatic compounds, particularly in the autoxidative regime. Additionally, the fuels that contained fewer n-alkanes exhibited greater pyrolytic stability.; There was also substantial evidence that the mechanism for pyrolytic deposit formation differs if dissolved oxygen is present or absent. Temperature-programmed oxidation profiles and scanning electron microscope images show that the deposit from the fuels has a different structure depending on the oxygen content of the starting fuels. This is especially obvious in the intermediate deposits. These differences are more pronounced in the deposits formed from the fuels consisting of hydroaromatic and aromatic compounds than in the deposits formed from the fuels consisting of naphthenic compounds.