The rates of peroxide formation in six model jet fuels were measured at various temperatures ranging from 43 to 120 °C with oxygen partial pressures ranging from approximately 10 to 1140 kPa. One of the fuels exhibited an increase in the rate of peroxide formation after alumina treatment, and three of the fuels showed induction periods. The results agreed with a kinetic model of the autoxidation process in that the peroxide concentration increased as the square of the stress duration. The rate of peroxide formation did not depend on the oxygen partial pressure. Arrhenius correlations of global rate constants determined from peroxide concentration time histories in accordance with the kinetic model showed that a single autoxidation mechanism explains the results obtained in the 43-120 °C temperature range. The results of this work encourage the development of a test method that predicts rate of peroxide formation at ambient conditions from data that may be obtained from more timely experiments at elevated temperatures.
As an alternative to established laboratory protocols, partial least-squares (PLS) regression models based on Fourier transform infrared (FT-IR) spectra were developed for the rapid and simultaneous determination of several middle distillate fuel properties. Requiring less than 2 mL of sample, the PLS models use a single wavelength range of baseline-uncorrected FT-IR spectra. Several preprocessing parameters were investigated, including mean-centering of the raw spectra and mean-centering of first- and second-difference spectra. In addition, modification to the calibration parameters included varying the number of cross-validation rotation samples from 5 to 50, applying a baseline correction to the spectra, and using restricted wavelength regions. In order to obtain an accurate estimate of the prediction error, we applied the method provided by Faber and Kowalski [Appl. Spectrosc. 51, 660 (1997)] that corrects for the measurement error in the reference values. On the basis of this work, the following middle distillate fuel properties may be confidently estimated by FT-IR: gravity, API°; density, g/mL; kinematic viscosity, cSt, 40 °C; boiling point at 50% recovery, °C; cetane index; carbon, wt %; hydrogen, wt %; carbon-to-hydrogen ratio, C/H; net heat of combustion, MJ/Kg (or BTU/lb); monocyclic aromatics, wt %; dicyclic aromatics, wt %; polycyclic aromatics, wt %; and total aromatics, wt %. Estimation of several other properties is also possible where reduced precision is acceptable.
Analytical methods for determining composition of new and used synthetic k~bricants have been developed as an important part of the Army's lubrication research effort. A logical approach for the systematic analysis of lubricants has been applied to a wide variety of selected military and commercial lubricants. Hybrid lubricant blends of synthetic hydrocarbons, esters, and mineral oils have been separated and analyzed through the combined use of spectroscopy and chromatopapt~y. Ester fractions have been fi~rther evaluuted by chen~ical hydrolysis and derivatization to determine exact composition of the parent acidic and alcoholic components. While characterization of lubricants to include more detailed additive compositionis not yet complete, expanded analytical approaches to provide compositional information for improved base stock definition have been enhanced.
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