A group-type analysis of hydrocarbons in a complex jet fuel may be more useful than attempting to analyze every component because the latter inevitably leaves a large portion of the fuel unidentified. While it may be difficult to accurately determine the identity of a particular compound, that compound can often be classified as belonging to a group or compound class because of its chromatographic retention and mass spectral properties. Compound class quantitation is often capable of relating compositional information to fuel properties. Two-dimensional gas chromatography (GC × GC) is a technique capable of providing this group-type separation and quantitation in jet fuels. This technique was used to examine a large set of fuels (Jet A, Jet A-1, JP-5, and JP-8, primarily) from petroleum sources and non-petroleum alternative sources, such as synthetic paraffinic kerosene (SPK). By comparing results from GC × GC analysis to established techniques and model compound studies, we have found that the accuracy of GC × GC for group-type analysis is excellent. Quantitation of group types for alternative fuel sources were also investigated and compared to conventional techniques. The possible uses and applications of group-type measurements using GC × GC for fuels and fuel-related materials are discussed.
High-performance liquid chromatography (HPLC) with electrospray ionization−mass spectrometry (ESI−MS) was used to identify several classes of heteroatomic, polar compounds containing oxygen, nitrogen, and sulfur in a variety of jet fuel samples. While nitrogen, oxygen, and sulfur compounds are present only at low concentrations in jet fuel, they contribute significantly to some important fuel properties. These trace, heteroatomic species can provide positive (e.g., improved lubricity) or negative (e.g., reduced thermal stability) impacts. Reversed-phase liquid chromatography with ESI−MS detection allows for the polar components to be selectively ionized and subsequently identified, despite the complex hydrocarbon fuel matrix. Phenols and carbazoles are detected in negative-ion [M − H] − mode, while anilines, pyridines, indoles, and quinolines are observed in positive-ion [M + H] + mode. Accurate mass measurements allow for the molecular formula of the polar components to be determined, while different structural classes of isomeric compounds could be determined via HPLC separation and the formation of derivatives. Derivatization shifts the retention time, species masses, and potentially, the ion charge formed of specific compound classes, allowing them to be positively identified. The usefulness and limits of HPLC with ESI−MS for quantitation of these fuel polar, heteroatomic species are also explored.
In recent years, the fuel system icing inhibitor (FSII) diethylene glycol monomethyl ether (DiEGME) has been implicated in an increasing incidence of peeling of topcoat material in the ullage space of integral wing tanks in the B-52 and other military aircraft. Work has indicated that, for the combination of DiEGME in JP-8 fuel, the icing inhibitor additive can concentrate in the tank ullage and condense at elevated concentrations on cooled tank walls. These high concentrations of DiEGME cause swelling and subsequent peeling of the epoxy-based topcoat. Here, we report on detailed studies of the compatibility of DiEGME and FSII replacement candidate triethylene glycol monomethyl ether (TriEGME) with BMS 10-39 fuel tank topcoat material. Tests were designed to simulate fuel tank wall exposures with subsequent topcoat degradation measured by icing inhibitor uptake analyses and pencil hardness evaluations. The lower volatility of TriEGME relative to the JP-8 fuel components results in it being less able to concentrate in the tank ullage and promote topcoat failure, as compared to DiEGME. This was confirmed with lower additive levels measured in the ullage, condensed vapors, and the exposed topcoat material. The pencil hardness of topcoat material exposed to fuel vapors was significantly improved upon changing from DiEGME to TriEGME exposure. Simulation experiments were able to reproduce the fuel tank topcoat peeling observed in the field as well as determine the conditions (concentration and temperature) required for topcoat degradation.
The autoxidation of jet fuel takes place via a complex free radical reaction mechanism that involves the decomposition of hydroperoxides.The liquid-phase, unimolecular decomposition of hydroperoxide has been isolated for experimental study. Three hydroperoxides relevant to jet fuel autoxidation, including cumene hydroperoxide (CHP), dodecane hydroperoxide (DHP), and ethylbenzene hydroperoxide (EBHP), were thermally decomposed separately and found to closely fit first-order behavior with respect to hydroperoxide concentration. The activation energy for liquid-phase thermolysis of these hydroperoxides was found to be significantly less than typical gas-phase values. Parameters affecting the rate of hydroperoxide decomposition, such as dissolved metal content, organic acids, and metal deactivator additive (MDA) were explored. Metal type was shown to be a significant factor affecting hydroperoxide decomposition rate, while naphthenic acids (NA) were shown to have little effect on the rate. However, when dissolved metal and NA were added together a strong synergistic effect on hydroperoxide decomposition rate was noted. The increases in decomposition rate due to dissolved metal and/or acid were effectively inhibited by treatment with MDA.
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