This project focuses on the compositional factors affecting high temperature thermal stability of coal-derived and petroleum-based jet fuels in pyrolytic regime. Thermal stability refers to the resistance of fuel to chemical decomposition at high temperatures to cause the solid deposition and liquid depletion. There are four broad objectives in this project, and the research work is divided into four tasks. The first task clarifies the chemistry of fuel degradation and mechanisms of solid formation, and identifying thermally stable classes of hydrocarbon compounds, and providing information for enhancing intrinsic stability of jet fuels. The second task involves characterization of the solids including deposits, sediments and gums produced from fuels and model compounds at high temperatures. The third task is to explore the means to enhance the thermal stability of fuels by examining the effects of various additives. The fourth task is a newly initiated exploratory study on conversion of coals to thermally stable jet fuels.

The focus of this study was on the autoxidation kinetics of deposit precursor formation in jet fuels. The objectives were: (1) to demonstrate that laser-induced fluorescence is a viable kinetic tool for measuring rates of deposit precursor formation in jet fuels; (2) to determine global rate expressions for the formation of thermal deposit precursors in jet fuels; and (3) to better understand the chemical mechanism of thermal stability. The fuels were isothermally stressed in small glass ampules in the 120 to 180 C range. Concentrations of deposit precursor, hydroperoxide and oxygen consumption were measured over time in the thermally stressed fuels. Deposit precursors were measured using laser-induced fluorescence (LIF), hydroperoxides using a spectrophotometric technique, and oxygen consumption by the pressure loss in the ampule. The expressions, I.P. = 1.278 x 10(exp -11)exp(28,517.9/RT) and R(sub dp) = 2.382 x 10(exp 17)exp(-34,369.2/RT) for the induction period, I.P. and rate of deposit precursor formation R(sub dp), were determined for Jet A fuel. The results of the study support a new theory of deposit formation in jet fuels, which suggest that acid catalyzed ionic reactions compete with free radical reactions to form deposit precursors. The results indicate that deposit precursors form only when aromatics are present in the fuel. Traces of sulfur reduce the rate of autoxidation but increase the yield of deposit precursor. Free radical chemistry is responsible for hydroperoxide formation and the oxidation of sulfur compounds to sulfonic acids. Phenols are then formed by the acid catalyzed decomposition of benzylic hydroperoxides, and deposit precursors are produced by the reaction of phenols with aldehydes, which forms a polymer similar to Bakelite. Deposit precursors appear to have a phenolic resin-like structure because the LIF spectra of the deposit precursors were similar to that of phenolic resin dissolved in TAM. Naegeli, David W. Glenn Research Center ...

Thermal stability and degradation of a commercial jet fuel were studied using an experimental rig developed recently. The apparatus consists of a fuel pre-heating section to simulate the usage of fuel as a coolant on aircraft, and a test section to simulate operating conditions found in aircraft injector fuel nozzles. Two independent diagnostic techniques, pressure drop measurements and carbon burn-off, were applied to assess carbon deposition produced within a test section. Parametric studies were performed to investigate the effect of test section inner diameter, test section material, and test section inlet temperature gradient on carbon deposition within the test section. It was determined that as the inner diameter of a test section increased, carbon deposition generally decreased. The axial location of maximum surface deposition moved downstream in a narrower test section. It was also found that solid carbon deposition decreased by increasing the test section inlet temperature gradient.

For technical readers in the aviation and fuel industries, and in testing laboratories, explores the history and philosophy of the thermal stability of aviation fuel, and considerations during the fuel's manufacture, storage and transport, use, and assessment. The 13 papers, representing a number of