1H and 13C NMR Analysis of Gas Turbine Fuels As Applied to the Advanced Distillation Curve Method

The analysis of gas turbine fuels by H-1 and C-13 nuclear magnetic resonance (NMR) spectroscopy as applied to the composition-explicit advanced distillation curve method is reported. To demonstrate the general applicability for such fuels, eight independent fuel samples were characterized: one sample of JP-S, one sample of JP-8, and six samples of Jet-A. Distillate fractions were obtained for each fuel by use of the advanced distillation curve (ADC) method. These fractions were analyzed by H-1 and C-13 NMR, along with the undistilled residue (i.e., the undistilled liquid remaining in the kettle after 90 vol % had been distilled) and the neat fuel. NMR spectroscopy is useful for the analysis of complex hydrocarbon mixtures because it provides the mole fractions of various classes of hydrocarbons, such as aromatics and linear alkanes, without the need to calibrate. NMR spectroscopy also gives ready access to other average properties for the components of each fuel sample, such as the extent and type of alkane branching. For example, the abundance of branch points at the beta position of aliphatic chains changes little for the various distillate fractions; however, branching on the interior of the aliphatic chains approximately doubles over the course of the distillation. For the heavier fractions of the fuel, interior branching becomes as important as branching at the beta and gamma positions. Such information is useful for the development of realistic fuel surrogates required for reliable thermophysical models. Finally, we compare the results obtained by NMR spectroscopy to previously reported GC MS and GC-FID analyses of the same fuel samples.