Ellipsometric Measurements of Alternative Fuels

Alternative jet fuels will be important in the future to ensure cleaner burning, reliable, and reasonably priced air transportation. One important property that must meet certification standards is the fuel\u27s thermal stability, or its ability to withstand heating before breaking down. Jet fuels are used as engine coolants, and thermally unstable fuels can form deposits in the fuel delivery systems, leading to a loss of fuel flow. In the past, the thermal stability of a fuel was rated using a color standard method. The color of the deposit left on a metal tube that had been heated and exposed to a test fuel were matched with a color standard to rate the level of deposition, and thus the fuel\u27s thermal stability. Ellipsometry, which is an optical technique that uses changes in a beam of light\u27s polarization after it reflects off a sample to determine the thickness of any film on that sample, has recently been implemented to improve the thermal stability characterization standard. Various aspects of the ellipsometric method have been investigated in this work. In addition, several thermal stability studies were carried out. The effect of increasing temperature on the thermal stability of Sasol Iso-Paraffinic Kerosene, Jet A, JP-8, and Gevo jet fuel have been analyzed, and the effect of varying levels of the additive naphthalene in Sasol IPK has also been investigated. Various theoretical optical models have been evaluated for their ability to predict deposit thickness. Finally, attempts to validate these measurements were made using scanning electron microscopy, ellipsometric tube rating, interferometric tube rating, and reference tubes. The analysis carried out in this work was used to make recommendations for improving the thermal stability test standard