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Two studies were conducted on the effects of the metal deactivator, N,N‘-disalicylidene-1,2-propanediamine (MDA) on jet fuel thermal stability. Study 1 focused on the effects of MDA on extended duration thermal stability testings ranging from 120 to 152 h. The test fuel was a Jet A, and the effects of MDA were examined with and without the addition of the antioxidant, BHT (2,6-di-tert-butyl-4-methylphenol) as well as with and without added copper. For study 2, the thermal stability test duration was 2.5 h, and the effect of time of addition of MDA, which was also investigated in study 1, was further examined in a test matrix that comprised two JP-5 fuels, two sources of copper, and three concentrations of MDA. Thermal stability was determined using the gravimetric JFTOT. The results of the extended duration testings indicate that even at the relatively high MDA concentrations examined (15 and 35 ppm), MDA exhibited a beneficial effect in the non copper doped commercial (Jet A) and Navy type fuel (Jet A + BHT). The results of the time of MDA addition studies indicate that early addition of MDA is more effective than late addition, for copper-contaminated stored jet fuels.

The effects of storage in the presence of copper using laboratory test conditions vs field conditions on fuel thermal stability were compared using five JP-5 fuels. Laboratory test conditions refer to accelerated storage at 90 °C/50 psig of air/24 h in the presence of soluble copper from copper(II) ethyl acetoacetate (CuEA). In contrast, field conditions refer to long-term storage at room temperature (∼20 °C) in the presence of dissolved copper from 90/10 copper-nickel (Cu-Ni) alloy for a period of approximately 6 months. Thermal stabilities were determined using the gravimetric JFTOT, which gives a quantitative measure of the total deposits formed. A copper concentration/storage effect was observed, which necessitated evaluations at similar copper concentrations. However, the source of copper appears not to be important. Instead, the main operative factor affecting the thermal stability of stored fuels appears to be the combination of long-term ambient storage and the presence of copper. Good agreement was obtained between the thermal stabilities of fuels that were stored using the specified laboratory and field conditions. These results are significant because (1) they validate the use of the specified laboratory test conditions as being realistic; (2) they support our premise that precursors that lead to thermal deposits are formed on storage in the presence of copper; and (3) they offer a rigorous method for predicting the potential thermal stabilities of jet fuels.

The capabilities of combustion performance predictors to reliably predict the sooting tendencies of aviation fuels in jet combustors were evaluated. The test matrix included two primary fuel sets which were representative of current and future aviation fuels and combustor data, which consisted of radiation and soot data from two different combustors at specific levels of operation. Four of the predictors evaluated were based on a single parameter, viz., three current predictors (smoke point, hydrogen content, and total aromatics content), and one new predictor, Shell's Premixed Burner Number. The remaining predictors, which were based on more than one parameter, include Rosfjord's correlation, Chin-Lefebvre's correlation, a smoke point-hydrogen content combination predictor, and, in addition, three new trial predictors, of which two were based on composition and one on a combination of differentiated aromatics content and smoke point. The results indicate two of the new trial predictors exhibited the best overall predictability. These two trial predictors are monocyclic aromatics important extensions of the parameters employed in Rosfjord's and Chin-Lefebvre's correlations, respectively. The better predictabilities of the two trial predictors are likely attributable to better weighting of the compositional contributions to sooting, particularly at the highest power demand.