OXIDATION OF JET FUELS AND THE FORMATION OF DEPOSITS

Jet fuels and et fuel surrogate were thermally stressed to simulate th e time-temperature history of aircraft fuel-handling systems. The resu lting fuels and soluble and insoluble products were analysed. The resu lts are shown to be incompatible with previous mechanisms concerning t he source of deposit precursors. In general, two important dependences on oxygen have been found: (1) in agreement with previous research, t he amount of deposit formed decreases significantly if oxygen is remov ed from the fuel before thermal stressing; (2) fuels that oxidize easi ly are likely to be more stable (as measured by deposits). New evidenc e is presented to support the free-radical mechanisms of oxidation and deposit formation, in contrast to proposed ionic mechanisms of oxidat ion. A general theory of oxidation of hydrocarbons has been incorporat ed to account for the observed oxygen-dependences, involving a free-ra dical, autoxidation, chain mechanism. It is proposed that the presence of naturally occurring antioxidant molecules plays an important role in both inhibiting the oxidation of the fuel and forming deposit precu rsors. Some properties (concentration, reactivity) of these antioxidan t molecules and the implications of the theory are discussed.