Effects of Temperature on Formation of Insolubles in Aviation Fuels

Ten aviation turbine fuels (five Jet-A fuels, three JP-5, one JP-8, and one JPTS) were stressed at 185 and 225°C in a single-pass heat exchanger. On the basis of several criteria applied at 185°C, these fuels cover a broad thermal-stability range from lesser-quality fuels to the most stable JPTS fuel. Three of these fuels contain significant concentrations of dissolved metal (copper, >30 ppb). The surface and bulk insolubles formed from each fuel have been quantified using surface-carbon burnoff of tubing sections and of in-line filters. The total insolubles measured at 185 and 225°C fall in the range 0.3–7.5 μg/mL, and 0.1–2 μg/mL, respectively. In general, the greater the quantity of insolubles formed at 185°C, the greater its reduction at 225°C. Possible explanations for this effect are offered, and implications relative to understanding surface fouling are discussed.