The dielectric constant of aviation turbine fuel is leveraged by aircraft fuel quantity indicator systems (FQISs) using the Clausius–Mossotti relation, which assumes no significant dipole moments. For fossil-derived jet fuel containing relatively consistent fractions of polar aromatic molecules, this is appropriate. However, the interest in sustainable aviation fuels (SAFs) to reduce the carbon intensity of commercial aviation has brought attention to the uncertainty of the FQISs’ compatibility for low- or zero-aromatic fuels exhibiting dielectric constant values outside of the conventional Jet-A range. A dielectric constant model accounting for the varying dipole moments of both aromatic and non-aromatic jet-range hydrocarbons improves the community’s understanding of fuel composition on FQISs’ operability and provides a tool suitable for fuel performance property optimizations while maintaining compatibility with current aircraft systems. Here, the Clausius–Mossotti relation is first evaluated against a training dataset of 240 dielectric constant and density measurements (48 neat hydrocarbons each measured at five temperatures). Then, the dipole moment is calculated for each species of interest using open-source computational chemistry software, and a second-degree binomial regression is performed over the training data to correct for the error in the Clausius–Mossotti relation. The Clausius–Mossotti relation exhibited an R² value of 0.54, which increased to 0.92 when terms for the dipole correction were added to the model. The improved accuracy from this model establishes a computationally inexpensive framework for modeling theoretical fuel compositions that demonstrate improved performance characteristics (sooting propensity, thermal management, aircraft efficiency, etc.) while remaining within key limiting property constraints, such as the dielectric constant.

Highly upgraded synthetic paraffinic fuels can exhibit marginal boundary lubricity because severe hydrotreating removes naturally occurring polar species that form protective surface films. Understanding which trace chemical classes drive this lubricity loss is essential for specification development for current blended and future 100% synthetic fuels. In this work, a HEFA-SPK matrix was systematically doped with representative sulfur-, oxygen-, and nitrogen-containing model compounds, and lubricity was measured by Ball-on-Cylinder Lubricity Evaluator (BOCLE, ASTM D5001). In parallel, neat hydrocarbons and commercial synthetic blending components (SBCs) were screened to isolate the role of bulk viscosity. Carboxylic acids were the most potent lubricity-restoring species, reducing wear scar diameter (WSD) below the 0.85 mm specification limit at oxygen-equivalent concentrations of only 1–2 ppm. The corresponding methyl ester produced only modest improvement. Heteroaromatic nitrogen compounds (indole, quinoline) required approximately 10 ppm fuel-bound nitrogen to reach the specification limit. Among sulfur species, a long-chain aliphatic thiol improved lubricity only at concentrations far exceeding jet-fuel sulfur limits, while aromatic sulfur compounds provided little benefit and could degrade lubricity at high concentrations. Viscosity showed a moderate correlation with WSD for neat hydrocarbons (R2 = 0.48) but none for real SBC fuels (R2 = 0.04). An inverse association between total acidity (ASTM D3242) and WSD further supports the dominant role of trace acidic oxygenates. These results provide a chemistry-based framework for managing lubricity in highly paraffinic fuels: assurance should target trace polar speciation or approved additives rather than bulk viscosity constraints.