PYROLYTIC DEGRADATION STUDIES OF A COAL-DERIVED AND A PETROLEUM-DERIVED AVIATION JET FUEL

The future high-Mach aircraft requires advanced jet fuel with high stability in rigorous thermal environments. In this work high-temperature thermal stability of two JP-8 type jet fuels, a petroleum-derived JP-8P and a coal-derived JP-8C was studied by stressing in closed reactors at 450-degrees-C under 0.7 MPa of N2 for periods ranging from 0.5 to 16 h. The extents of fuel degradation in terms of liquid depletion, gas formation, and solid deposition were always higher with JP-8P than with JP-8C. There appeared an induction period for solid formation, which was longer for JP-8C than for JP-8P. Tests with the saturates isolated chromatographically from these fuels indicated that JP-8C saturates are much more stable than the JP-8P saturates, and the higher stability of JP-8C is due to its composition. JP-8C is rich in one- to three-ring cycloalkanes and two-ring hydroaromatics, while JP-8P is composed mainly of long-chain paraffins. GC-MS provided valuable information on the relative stability and molecular transformation of hydrocarbon components in these jet fuels. Cycloalkanes; were found to be more stable than long-chain paraffins with the same carbon number. The stability decreases with increasing length of main chain for the long-chain paraffins, or side chain for alkylcycloalkanes. Multisubstituted cycloalkanes are more stable than the monosubstituted ones with the same carbon number. Steric conformation of cycloalkanes also affects their reactivity; for decalin, the trans isomer was found to be more stable than the cis isomer. The higher stability of JP-8C can be attributed mainly to its higher content of cycloalkanes. Tetralins and decalins present in JP-8C also contribute to capping the thermally generated reactive radicals by hydrogen donation.