Ignition behavior and surrogate modeling of JP-8 and of camelina and tallow hydrotreated renewable jet fuels at low temperatures

The autoignition characteristics of the conventional jet fuel, JP-8, and the alternative jet fuels, camelina and tallow hydrotreated renewable jet (HRJ) fuels, are investigated using a rapid compression machine and the direct test chamber charge preparation approach. Ignition delay measurements are made at low compressed temperatures (625. K. T_c. 730. K), compressed pressures of p_c=5, 10, and 20. bar, and equivalence ratios of φ=0.25, 0.5 and 1.0 in air. The HRJ fuels ignite more readily than JP-8 for all tested conditions, consistent with derived cetane number data in the literature. The camelina and tallow HRJ fuels exhibit similar autoignition characteristics, but the two fuels can be distinguished under stoichiometric conditions. Kinetic modeling is conducted with a 2-component surrogate (10% n-dodecane/90% 2-methylundecane) and a single component surrogate (2-methylnonane) to evaluate the potential to predict ignition behavior of the HRJ fuels. Modeling results indicate that the surrogate fuels can only provide useful predictions at a limited set of conditions (p_c=5. bar and φ=1.0), and that the agreement of the model and experimental data improves with decreasing compressed pressure. Under most conditions, the 2-component surrogate provides better prediction of ignition behavior, but the single component surrogate is superior at low pressures near the negative temperature coefficient region.