When some elastomer (rubber) compounds, and specifically those used for seals in fuel-wetted components of vehicles and equipment, are suddenly "switch-loaded" from a fuel of given composition to one of a somewhat different composition, swell/shrink issues relating to seal performance may arise, possibly leading to fuel leakage. The key objective of this study was to evaluate what happens to the elastomers with sudden switches from a conventional (petroleum-derived) fuel to a synthetic

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... atic) paraffinic fuel produced from natural gas using gas-to-liquids (GTL) and Fischer-Tropsch (FT) synthesis processes with or without surrogate aromatics. Results from this evaluation indicate that, for the nitrile elastomers evaluated, relatively large swings in swell occur with switches between fuels of varying levels of aromatic content and the synthetic aviation turbine fuel containing no aromatics. These observations support the conclusion that impact on the nitrile elastomer when switch-loading synthetic (non-aromatic) and petroleum-derived fuel, is highly dependent on aromatic hydrocarbon type and concentration.