Low-Temperature Properties of Renewable High-Density Fuel Blends

The low-temperature properties of high-density terpene dimer fuels and fuel mixtures with JP-8, JP-10, and hydrogenated pinene have been studied by shear viscometry and thermomechanical analysis (TMA). Neat terpene dimers have a viscosity of 3.94 × 103 mPa·s at −10 °C, while 50:50 mixtures with JP-10, RJ-4, pinane, and JP-8 have viscosities 2–3 orders of magnitude lower at 23.9, 53.0, 24.9, and 3.7 mPa·s, respectively. Linear and branched alkanes in JP-8 disrupt glass formation of the dimers, explaining the significant difference between the viscosity afforded by bicyclic diluents and JP-8. To complement the viscosity data, TMA was used to observe low-temperature transitions (Tm and Tg) of the blended fuels. Mixtures of the terpene dimers with cyclic molecules show only glass transition temperatures with no observable melting points, while mixtures with JP-8 and decane show Tg values that transition to melting points at high concentrations of terpene dimers. The results suggest that blending conventional fuels with terpene dimers is an effective strategy for mitigating the high viscosity of the C20 molecules. In addition, blending these renewable fuels with conventional jet fuel (JP-8) imparts both a higher density as well as an improved volumetric net heat of combustion while maintaining an acceptable low-temperature viscosity when compared to JP-8 alone.