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Thermal stressing of a Jet A fuel containing triphenylphosphine (TPP) as an additive results in a significant enhancement in thermal oxidative stability. Efforts to elucidate the mechanism(s) responsible for the observed thermal oxidative stability enhancement are reported. Data presented for the reaction of TPP with molecular oxygen show two pathways to be important. In particular, in nonpolar solvents and in the presence of BHT, the data are consistent with TPP playing an oxygen scavenging role via operation of an electron-transfer-initiated-oxygenation chain mechanism. The significances of these findings to the potential development of a new generation of thermal oxidative stability enhancing additives is discussed.

A quartz crystal microbalance (QCM)/Parr bomb system with a headspace oxygen sensor is used to measure oxidation and deposition during thermal oxidative stressing of jet fuel. The advantages of the oxygen sensor technique in monitoring fuel oxidation is demonstrated. Simultaneous measurement of deposition using the QCM shows a strong correlation between oxidation and deposition in jet fuels. Studies performed over the temperature range 140 to 180°C show that surface deposition peaks at an intermediate temperature, while bulk deposition increases with temperature. In studies of jet fuel antioxidants, we find that rapid increases in oxidation rate occur upon consumption of the antioxidant. The antioxidant appears to be consumed by reaction with alkylperoxy radicals. In studies of metal deactivator (MDA) additives, we find that MDA is consumed during thermal stressing, and this consumption results in large increases in the oxidation rate of metal containing fuels. Mechanisms of MDA consumption are hypothesized.

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