Influence of Storage Conditions, Sample Handling, Sample Preparation, and Repeated Analysis on the Measured Flash Point and Hydrocarbon Composition of Jet A

Abstract

Chemical and physical properties of jet fuel can change during storage or transportation, potentially rendering the fuel unsafe or unsuitable for use. Thus, it is crucial that the chemical and physical properties determined for a jet fuel accurately represent its properties. The goal of this study was to determine how storage conditions, sample handling, sample preparation, and repeated analysis of a Jet A fuel affects its hydrocarbon composition and flash point. The former was determined via comprehensive two-dimensional gas chromatography with flame ionization detection (GC × GC/FID) and the latter via a Tag closed-cup flash point tester. The following experiments were performed to explore possible changes in the above properties: (1) storage for up to 24 weeks at room temperature in three different types of closed containers (mason jars, amber glass bottles, and F-style cans); (2) storage for up to 24 h in the same containers but with the container cap removed; (3) storage of samples prepared for GC × GC/FID analysis for 1–7 days at room temperature, in a refrigerator, or in a freezer prior to analysis; and finally, (4) repeated GCxGC/FID analysis of a given sample vial compared to analysis of several identically prepared sample vials just once. The effects of the choice of the signal-to-noise ratio (S/N) threshold on the precision of the GC × GC/FID measurements and the number of peaks detected in each chromatogram were examined. Further, the percentage of the peak areas included in quantitation when using different S/N thresholds was also investigated and an optimal S/N threshold value was determined. The hydrocarbon compositions and flash point values determined for the Jet A samples stored for up to 24 weeks in a similar container were very similar. However, a relationship was observed between the similarity of the flash point values and the hydrocarbon compositions and the type of capped storage container used. The flash point values and hydrocarbon compositions were most similar for the fuels stored in mason jars and least similar for the fuels stored in F-style cans. Furthermore, substantial differences were observed in the flash point values (increases of 1.6–5.6 °C after 24 hours) and hydrocarbon compositions (percentage decreases of 3.02–13.26% after 24 hours in the wt. % of the most volatile compounds) for the fuels stored in uncapped containers, especially mason jars. Only very minor changes were observed in the hydrocarbon composition when samples were prepared for GC × GC/FID analysis 1–7 days prior to analysis, regardless of the temperature or duration of storage. The number of injections made from each sample vial for GCxGC/FID analysis proved to influence the hydrocarbon composition as the weight percent (wt. %) of the most volatile hydrocarbons was reduced and the number of peaks with S/N values greater than the S/N threshold was increased with the number of injections.