EVALUATION OF THE EFFECTIVENESS OF A METAL DEACTIVATOR AND OTHER ADDITIVES IN REDUCING INSOLUBLES IN AVIATION FUELS

Surface fouling in aircraft fuel lines resulting from autoxidation of aviation fuel leads to reduced efficiency as deposits collect on heat exchangers, nozzles, and servocontrols and may ultimately lend to syst em failure. Metal surfaces and trace quantities of metals dissolved in the fuel exacerbate the surface-fouling problem because they can cata lyze free-radical initiation, thereby accelerating autoxidation. Addit ives and additive packages containing antioxidants, dispersants, and m etal deactivators (MDA) have been shown to reduce insolubles in some f uels. Because of metal chelation and possible metal-surface passivatio n, MDA has been proposed as an additive component to be included in al l fuels, even those without dissolved metals. The goal of the present study was to obtain fundamental information on the behavior of MDA und er conditions where surface-passivation effects are minimal. Experimen ts have been conducted to (1) study the effects of adding MDA to fuels containing a significant concentration of dissolved metals (i.e., che lation) and to those containing minor concentrations of dissolved meta ls and (2) investigate interactions when MDA is used in conjunction wi th an antioxidant and a dispersant. Simple fuel-line-fouling simulatio ns with a single-pass tubular heat exchanger operated under near-isoth ermal conditions have been conducted to study the thermal behavior at 185 degrees C of several neat and MDA-treated jet fuels as well as fue ls treated with MDA plus other additives. Comparison of neat and treat ed fuels is based on several criteria: (1) dependence of autoxidation on stress duration, (2) dependence of surface deposition on stress dur ation, and (3) quantity of total insolubles (bulk filterables and surf ace deposits). potential advantages and disadvantages of using MDA alo ne and in combination are discussed.