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.

Measurements of the densities, viscosities, and speeds of sound of binary mixtures of n-tridecane and n-alkylcyclohexanes (methyl-, ethyl-, butyl-, pentyl-, heptyl-, octyl-, decyl-, and dodecylcyclohexanes) are reported at various mole fractions. Mixture densities, viscosities, and speeds of sound increased with a decrease in temperature and an increase in the component with the higher property value. Excess molar volumes (V m E’s) decreased with increasing alkyl chain length on the n-alkylcyclohexanes. The excess speeds of sound (c E’s) decreased as the n-alkyl chain length decreased until a minimum was reached for ethylcyclohexane, and then it increased for methylcyclohexane. For all molecules tested except methylcyclohexane, V m E’s and excess isentropic compressibilities (K s E’s) had the same sign, suggesting that the amount of space taken up by the molecules was influencing compressibility. Methylcyclohexane, however, had the largest positive V m E, but its excess compressibility was negative and close to zero. Its extra space was not more compressible. The V m E’s, c E’s, and viscosity deviations for n-tridecane mixtures fell between those reported for n-dodecane and n-hexadecane. These data and trends can be used by fuel researchers who are formulating mixtures to represent various fuels.

The viscosities and densities ((293.15 to 353.15) K), speeds of sound ((293.15 to 333.15) K), surface tensions (room temperature), and flash points were measured for binary mixtures of n-butylcyclohexane with either toluene or n-hexadecane. Increasing the temperature decreased the densities, and the excess molar volumes of the mixtures were generally positive, suggesting increased spacing due to differences in packing and intermolecular forces. Increasing the temperature also decreased the viscosities, and the McAllister three-body model successfully modeled the viscosity with the larger fitting term corresponding to two molecules of the more viscous substance. The mixture surface tensions and flash points fell between the pure-component values, which ranged from (26.7 to 28.6) mN•m −1 and (324.7 to 406.2) K, respectively. The speed of sound decreased with increasing mole fraction of n-butylcycylohexane in nhexadecane, but several speed of sound values for mixtures of n-butylcyclohexane and toluene were lower than those of either component. For both sets of mixtures, the isentropic bulk moduli of several mixtures were lower than those of their components. These results show that simple blending rules cannot be used to predict the speed of sound and bulk modulus of these mixtures.

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.