Oxygen Diffusion through JP-8 as Related to Thermal-Oxidative Coking and Titania-Based Remediation Measures

Thermal oxidative coking in jet engine injector passages leads to costly maintenance procedures as well as a significant decrease in engine efficiency. Research has shown that removing dissolved oxygen from the fuel before it reaches a heated passage can result in 1/70th of the coke buildup in injector passages [1]. However, the concern is that the high pressure, high temperature environment of an engine’s combustion chamber will cause the fuel to re-oxygenate rapidly, negating any positive effects of the de-oxygenating process. In connection with attempting to better understand and find solutions to the re-oxygenation leading to coking problem, the objective of this work was twofold. First, to develop a better understanding of the rates and important factors in the re-oxygenation of common jet fuels (Jet A, JP-8, etc.), where computer models and representative physical tests aided the education of the important parameters. The second focus was then on mitigating the effects of the re-uptake of oxygen. In particular, the possible use of titanium dioxide (titania, TiO2) nano-structures within the injector passage are being studied for their potential anti-coking properties. Titania structures have been shown to render a surface oleophobic [2, 3, 4] (i.e. able to readily shed oils), and, separately, able to photocatalytically decompose coke when exposed to UV irradiation [5, 6]. Theoretically, if the oleophobic and photocatalytic behaviors of titania were combined within a single passage, an injector could be manufactured such that shutting off individual injectors within a large injector array during low power demand periods (i.e. cruise or idle) would not run the risk of coking because there would be limited fuel to re-oxygenate and the small amount of coke build up would be passively removed