| Jet fuels are exploited as coolants in military aircraft to dissipate heat loads generated from a variety of components and subsystems. At temperatures near and above 140°C liquid fuels chemically react via an autoxidation chain mechanism with the dissolved oxygen present from exposure to air, yielding the production of detrimental surface deposits. Previously, there have been no means to predict such behavior and progress in deposition modeling has been empirically-driven. In this dissertation, a modeling capability to predict jet fuel thermal oxidation and deposition processes is established. The research consisted of three major steps that were performed in sequence to develop and validate the model. The first step was an assessment of chemical kinetic mechanisms in their ability to simulate, with quantitative accuracy, dissolved oxygen consumption over a range of experimental conditions for a paraffinic mixture with oxidation characteristics representative of severely hydrotreated jet fuel. The second step was the introduction of measurable species classes, or groups of compounds, as a means to distinguish jet fuel samples in the kinetic mechanism. In addition to the consumption of dissolved oxygen, the production and consumption of fuel hydroperoxide species simulated by the kinetic mechanism is assessed. The third step was an evaluation of the refined mechanism and measurement-based method to distinguish fuel samples in computational fluid dynamics simulations of deposit formation occurring in near-isothermal (185°C) and non-isothermal (20--400°C) flowing environments. All reactions and rate parameters of the resulting model are fixed, all inputs to the model are based on unstressed fuel composition measurements, and the model has been validated over a wide range of samples and experimental conditions. Thus, a priori estimates of jet fuel thermal oxidation and deposition behavior may be obtained. |
