Thermophysical properties (densities, speeds of sound, bulk moduli, and viscosities) of binary mixtures of n-dodecane with n-alkylcyclohexanes (propyl- to dodecylcyclohexane) were examined at various compositions and temperatures (293.15–333.15 K). Viscosities were analyzed using the McAllister three-body equation, and excess molar Gibbs energies of activation for viscous flow (ΔG*E) at 293.15 K were calculated. Because the ΔG*E values did not differ significantly from zero, the mixtures appear to behave ideally. In contrast, nonzero excess molar volume values obtained both experimentally and using molecular dynamics (MD) simulations suggest nonideal behavior. Excess molar volumes were the most negative for n-dodecylcyclohexane mixtures and increased with decreasing alkyl side-chain length eventually becoming slightly positive for mixtures containing n-propylcyclohexane. MD simulations were able to predict density, isentropic bulk modulus, and dynamic viscosity values, but the accuracy of the calculated densities decreased slightly with increasing temperature. Voronoi tessellation was used to calculate histograms of molecular volumes in the mixtures. The most probable volume of n-dodecane increases or decreases when mixed with n-propylcyclohexane or n-dodecylcyclohexane, respectively. These shifts in molar volume are responsible for the expansion and contraction upon mixing observed in the excess molar volume data. Volume contraction (negative excess molar volume) produces mixture speeds of sound that are faster than ideal (positive excess speed of sound) unless confounded by opposing compressibility differences. Excess speeds of sound were positive for n-dodecylcyclohexane mixtures, decreased as the alkyl side-chain length increased, and were negative for n-propylcyclohexane mixtures.

The physical properties of direct sugar to hydrocarbon diesel (DSH-76) and several binary mixtures of n-hexadecane and 2,2,4,6,6-pentamethylheptane were measured in this work. The density and viscosity were measured at temperatures ranging from (293.15 to 393.15) K, and the pure component values fell within the range of previously reported values. Speed of sound data at temperatures ranging from (293.15 to 323.15) K increased from (1089 to 1357) m•s −1 . The bulk modulus was calculated from the density and speed of sound data, and its values ranged from (858 to 1425) MPa. Flash point values ranged from (318 to 408) K, and the surface tension values ranged from (21.8 to 27.3) mN•m −1 . The values of density, viscosity, speed of sound, bulk modulus, flash point (378 K), and surface tension (25.0 mN•m −1 ) for the DSH-76 fell within the range of values measured for the binary mixtures of nhexadecane and 2,2,4,6,6-pentamethylheptane. These data suggest that a binary mixture of n-hexadecane and 2,2,4,6,6pentamethylheptane may be a suitable surrogate for renewable fuels such as DSH-76.

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.

This work reports densities, speeds of sound, and viscosities of binary mixtures of n-alkylcyclohexanes (propyl- to dodecylcyclohexane) in n-hexadecane as a function of temperature. Isentropic bulk moduli for these mixtures were calculated from these speed of sound and density data. Mixture densities increased with increasing alkylcyclohexane concentration. As the alkyl-chain length on the alkylcyclohexane increased, the excess molar volume decreased, with n-propylcyclohexane and n-dodecylcyclohexane mixtures having positive and negative excess molar volumes, respectively. Molecular dynamics simulations accurately predict densities and isentropic bulk moduli of n-propylcyclohexane and n-dodecylcyclohexane mixtures, and suggest that the differences in excess molar volumes for different alkyl-chain lengths are related to changes in molecular packing. The speed of sound as a function of mole fraction was modeled using a second-order polynomial, and viscosities were modeled using the McAllister three-body equation. Excess speeds of sound and excess molar Gibbs energies of activation for viscous flow at 293.15 K were not statistically different from zero, which suggest ideal behavior. Many of these mixtures have densities similar to those of petroleum-based diesel and jet fuel and viscosities comparable to diesel fuel. The isentropic bulk modulus of jet fuel is best matched by mixtures of n-propylcyclohexane, while that of diesel fuel is matched by mixtures of n-decylcyclohexane or n-dodecylcyclohexane.

In this work, the physical properties of binary mixtures of n-dodecane with 2,2,4,6,6-pentamethylheptane or 2,2,4,4,6,8,8-heptamethylnonane were measured and compared to properties of four hydrotreated renewable jet (HRJ) and hydrotreated renewable diesel (HRD) fuels. Density and viscosity were measured at temperatures ranging from (293.15 to 393.15) K, and the speed of sound was measured at temperatures ranging from (293.15 to 333.15) K. For the mixtures, the speed of sound at 293.15 K decreased (1297.6 to 1285.7) m•s −1 as the mole fraction of 2,2,4,4,6,8,8heptamethylnonane increased and decreased (1297.6 to 1203.6) m•s −1 as the mole fraction of 2,2,4,6,6-pentamethylheptane increased. The bulk modulus was calculated from density and speed of sound data. Flash points for the mixtures ranged from (318 to 367) K, and surface tension values ranged from (21.8 to 25.3) mN•m −1 . When comparing to alternative fuels, two-component mixtures could be found to match the density and viscosity of HRJs and HRDs. The mixtures matched the speed of sound, bulk modulus, surface tension, and flash point of some of these hydrotreated fuels. These data suggest that binary mixtures of n-dodecane with branched alkanes may be suitable surrogates for renewable fuels.

In this study, the chemical composition and physical properties of an algal-based hydrotreated renewable diesel (HRD) fuel were used to develop a surrogate mixture containing commercially available hydrocarbons. Analysis of the chemical composition of the algal HRD showed a small quantity of low-molecular-weight components and a high quantity of four high-molecular-weight components: n-pentadecane, n-hexadecane, n-heptadecane, and n-octadecane. Using these four components, a fifth branched component was added to match the physical properties of the algal HRD. Candidates for the fifth component were 2-methyloctane, 2-methylnonane, isooctane, and isododecane. The isooctane- and isododecane-based surrogates were tested in a Yanmar engine along with algal HRD and petroleum F76 diesel to assess the start of ignition, start of combustion, ignition delay, maximum rate of heat release, and overall combustion duration. The surrogate that best matches the physical properties of the flash point, density, viscosity, and surface tension as well as most closely reflecting the combustion metrics is one containing isododecane, n-pentadecane, n-hexadecane, n-heptadecane, and n-octadecane.

In the caption of Figure 13, "Injection delay" should be "Ignition delay".

In this study, the chemical composition and physical properties of an alcohol-to-jet (ATJ) fuel were used to develop a surrogate mixture containing commercially available hydrocarbons. Analysis of the chemical composition of the ATJ showed a high quantity of two specific branched alkanes (2,2,4,4,6,8,8-heptamethylnonane and 2,2,4,6,6-pentamethylheptane) and a small quantity of other branched alkanes that are isomers of these two alkanes. Surrogate mixtures containing 2,2,4,4,6,8,8-heptamethylnonane and a mixture of isododecane isomers were prepared to determine what composition would match the density, viscosity, speed of sound, bulk modulus, surface tension, and flash point of ATJ. The optimal surrogate contained a 0.25 mass fraction of 2,2,4,4,6,8,8-heptamethylnonane in isododecane isomers. Combustion experiments were then conducted in a Yanmar diesel engine with fuel mixtures containing 70% (by volume) petroleum jet fuel with 30% ATJ, 2,2,4,4,6,8,8-heptamethylnonane, the optimal surrogate mixtures based on physical properties, or the isododecane isomers. The startup performances of the three 30% surrogate mixtures were very similar to that of the 70% JP-5 with 30% ATJ fuel. No significant differences were seen in the engine combustion characteristics of the three 70/30 surrogates, as compared to the base 70% JP-5/ 30% ATJ fuel mixture. These results show that a surrogate mixture has been successfully prepared that matches the physical and chemical properties and combustion behavior of an ATJ fuel.