Surrogate fuel mixtures for a hydrodepolymerized cellulosic diesel (HDCD) fuel were formulated based on HDCD's physical properties and chemical composition. HDCD was found to contain alicylic, cyclic, and aromatic compounds. Surrogate mixtures composed of trans-decahydronaphthalene (trans-decalin) and 1,2,3,4-tetrahydronaphthalene (tetralin) matched HDCD's speed of sound, density, and bulk modulus. Diesel engine experiments were conducted on mixtures containing petroleum diesel fuel (60 and 80% volume fraction) mixed with HDCD, tetralin, trans-decalin, or a mixture with 0.42 mass fraction of tetralin in trans-decalin. At both volume fractions, the start-up performance of the two-component surrogate/ petroleum fuel mixtures matched that of HDCD/petroleum mixtures. The trans-decalin/petroleum fuel mixtures started faster while the tetralin/petroleum fuel mixtures started more slowly than those containing HDCD. These results show that speed of sound, density, and bulk modulus can be used as metrics to design surrogate fuel mixtures that match fuel start-up performance in diesel engines.

The viscosities and densities (293.15−373.15 K), speeds of sound (293.15−333.15 K), surface tensions (room temperature), and flash points were measured for binary mixtures of n-hexadecane and alkylbenzenes (hexylbenzene, octylbenzene, dodecylbenzene), which are components of diesel fuel. Increasing the temperature decreased densities, and excess molar volumes of mixtures were higher for hexylbenzene mixtures than for octylbenzene mixtures and insignificantly different from zero for dodecylbenzene mixtures. The decrease in excess molar volume with increasing alkyl chain length is consistent with other binary mixtures of n-hexadecane and alkylbenzenes. Increasing the temperature decreased viscosities, and the McAllister three-body model successfully modeled viscosity with the compound in the mixture with the highest individual viscosity having the largest fitted interaction parameter. Mixture flashpoints, speed of sounds, bulk moduli, and surface tensions fell between the pure component values. For n-hexadecane/n-hexylbenzene mixtures, as the mole fraction of hexylbenzene increased, the speed of sound remained constant until a mole fraction of 0.5; then the speed of sound increased. On the basis of these data, binary mixtures of these compounds could be formulated to have property values that match those found in diesel fuel, except for surface tension, and thereby be potential fuel surrogates.

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)Q MS) and advanced two-dimensional gas chromatography/(electron ionization) high resolution time-of-flight mass spectrometry (GC×GC/(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 nbutylbenzene 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) threecomponent 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.