High-Resolution Mass Spectrometry Reveals Heteroatom-Based Compositional Trends Linked to Jet Fuel Instability

When exposed to high heat, the nitrogen- and oxygen-containing compounds (NCCs and OCCs, respectively) in fuels react to form oxidative deposits that may result in fuel failures. Due to the complexity of fuel, it is arduous to assign which class(es) of NCCs and OCCs exhibit the greatest propensities to form these adverse deposits. Hence, there is a burgeoning need to qualitatively characterize stable and thermally unstable jet fuels and compare their compositions. If links between compositions and fuel stability are realized, the harmful compounds can be identified and targeted for removal, consequently improving the fuel quality. The central aims of this work were to (1) qualitatively characterize ionized NCCs and OCCs derived from stable and unstable jet fuels, (2) compare and contrast the NCC and OCC compositions of stable and unstable fuels, (3) denote links between composition and thermally unstable fuels, and (4) utilize automated cluster optimization via serial variable down-selection and singular value decomposition to confirm manual assessments of data linkages. To complete the characterization, (+) and (−) electrospray ionization coupled to a high-resolution Orbitrap mass spectrometer was utilized. Upon measurement, the unstable fuels had greater abundances of OCCs with ≥2 oxygen atoms and ions with empirical formulas of CnH(2n-1)O2, CnH(2n-3)O2, and CnH(2n-5)O2. Furthermore, although stable fuels contained a balanced distribution of different classes of NCCs, unstable fuels had a relatively large abundance of ions with a specific empirical formula of CnH2n-6N. Additional qualitative information was reported, including Kendrick Mass Defect plots. Overall, NCC and OCC compositional differences were noted when stable and unstable fuels were compared, highlighting the proficiency of the Orbitrap at characterization. Although it remains uncertain if these differences are responsible for fuel failure, the emergence of links between fuel compositions and thermal instability may prove critical at identifying the class(es) that pose the most harm to fuel.