Analysis of Catalytic Hydrothermal Conversion Jet Fuel and Surrogate Mixture Formulation: Components, Properties, and Combustion

Chemical analysis and property measurements of a catalytic hydrothermal conversion jet (CHCJ) fuel were used to formulate hydrocarbon mixtures for use as fuel surrogates. Using conventional gas chromatography/(electron ionization) quadrupole mass spectrometry (GC/(EI)QMS) and advanced two-dimensional gas chromatography/(electron ionization) high resolution time-of-flight mass spectrometry (GCxGC/(EI)TOF MS), CHCJ was found to differ from Jet-A fuel and to contain mostly linear alkanes, alkylcyclohexanes, and alkylbenzenes, with small amounts of branched alkanes and multiring aromatic compounds. Various surrogates were prepared containing n-dodecane, n-butylcyclohexane, and n-butylbenzene, and their density, viscosity, speed of sound, surface tension, and derived cetane number (DCN) were measured to determine the compositions that most closely matched that of the CHCJ. The optimal surrogates were (1) n-butylcyclohexane, (2) 0.64 mole fraction of n-butylbenzene in n-dodecane, and (3) three three-component blends of n-butylcyclohexane, n-butylbenzene, and n-dodecane with ratios of n-dodecane to n-butylcyclohexane of 0.25, 0.50, and 0.75 corresponding to a lower, medium, and higher n-butylbenzene concentration. Since fuel logistics in the military could be greatly simplified by use of a single fuel for both jet and diesel engines, this study examined this alternative jet fuel and its potential surrogates with respect to combustion in a diesel engine. Combustion experiments using a Waukesha diesel Cooperative Fuels Research (CFR) engine showed that all surrogate mixtures emulated the combustion engine performance of CHCJ in the areas of thermal efficiency, ignition delay, relative rate of heat release, crank angle degree 50% fuel burned location, and burn duration. All the surrogate mixtures operated in the Waukesha engine all showed statistically similar performance to the CHCJ fuel; however, the midaromatic (n-butylbenzene) three component surrogate was marginally closer than either the higher or lower aromatic blends. These results show that DCN and other physical property measurements of a jet fuel can be used in conjunction with chemical composition to design surrogate fuel mixtures that match jet fuel performance in a diesel engine. These surrogate mixtures can be used in modeling studies to help determine the aspects of jet fuels that would enable them to have acceptable performance in a military diesel engine.