In this study, a novel approach was developed to formulate surrogate fuels having characteristics that are representative of diesel fuels produced from real-world refinery streams. Because diesel fuels typically consist of hundreds of compounds, it is difficult to conclusively determine the effects of fuel composition on combustion properties. Surrogate fuels, being simpler representations of these practical fuels, are of interest because they can provide a better understanding of fundamental fuel-composition and property effects on combustion and emissions-formation processes in internal-combustion engines. In addition, the application of surrogate fuels in numerical simulations with accurate vaporization, mixing, and combustion models could revolutionize future engine designs by enabling computational optimization for evolving real fuels. Dependable computational design would not only improve engine function, it would do so at significant cost savings relative to current optimization strategies that rely on physical testing of hardware prototypes. The approach in this study utilized the stateof-the-art techniques of 13 C and 1 H nuclear magnetic resonance spectroscopy and the advanced distillation curve to characterize fuel composition and volatility, respectively. The ignition quality was quantified by the derived cetane number. Two wellcharacterized, ultra-low-sulfur #2 diesel reference fuels produced from refinery streams were used as target fuels: a 2007 emissions certification fuel and a Coordinating Research Council (CRC) Fuels for Advanced Combustion Engines (FACE) diesel fuel. A surrogate was created for each target fuel by blending eight pure compounds. The known carbon bond types within the pure compounds, as well as models for the ignition qualities and volatilities of their mixtures, were used in a multiproperty regression algorithm to determine optimal surrogate formulations. The predicted and measured surrogate-fuel properties were quantitatively compared to the measured target-fuel properties, and good agreement was found.

The chemical complexity and diversity of an Athabasca asphaltene sample was described using a series of molecular representations. The molecular representations were created with a Monte Carlo construction method that represented molecules with a series of aromatic and aliphatic groups. After the groups were randomly sampled for a molecule, a connection algorithm linked them together to form molecules consisting of aromatic groups connected by aliphatic chains and thioethers. A sequential nonlinear optimization algorithm was used to select a small subset of molecules that were consistent with elemental, molecular weight, and NMR spectroscopy (both 13C and 1H) data. To accurately represent the analytical data for the asphaltene sample, a minimum of five molecules was needed. On the basis of the results of the sequential optimization, at least 50 molecules in the starting population were required to produce an analytically consistent molecular representation.

The primary objectives of this work were to formulate, blend, and characterize a set of four ultralow-sulfur diesel surrogate fuels in quantities sufficient to enable their study in single-cylinder-engine and combustion-vessel experiments. The surrogate fuels feature increasing levels of compositional accuracy (i.e., increasing exactness in matching hydrocarbon structural characteristics) relative to the single target diesel fuel upon which the surrogate fuels are based. This approach was taken to assist in determining the minimum level of surrogate-fuel compositional accuracy that is required to adequately emulate the performance characteristics of the target fuel under different combustion modes. For each of the four surrogate fuels, an approximately 30 L batch was blended, and a number of the physical and chemical properties were measured. This work documents the surrogate-fuel creation process and the results of the property measurements.

After successful isolation of the most interfacially active subfraction of asphaltenes (IAA) reported in part one of this series of publications, comprehensive chemical analyses including ES-MS, elemental analysis, FTIR and NMR were used to determine how the molecular fingerprint features of IAA are different from those of the remaining asphaltenes (RA).Compared with RA, the IAA molecules were shown to have higher molecular weight and higher contents of heteroatoms (e.g., three times higher oxygen content). The analysis on the elemental content and FTIR spectroscopy suggested that IAA contained a higher content of high polarity sulfoxide groups which were not present in the RA. The results of ES-MS, NMR, FTIR and elemental analysis were used to construct average molecular representations of IAA and RA molecules. These structures were used in molecular dynamic (MD) simulation to study interfacial and aggregation behaviors of the proposed representative molecules. MD simulation study showed little affinity of representative RA molecules to the oil/water interface while the representative IAA molecules had a much higher interfacial activity, which corresponds to the extraction method. The aggregation of IAA molecules in the bulk oil phase and their adsorption at oil/water interface were not directly related to the ring system but rather to the associations between or including sulfoxide groups. The IAA molecules self-assembled in solvent, forming supramolecular structures and a porous network at the oil/water interface as suggested in our previous work. The results obtained in this study provide a better understanding of the role of asphaltenes in stabilizing petroleum emulsions.

We examine the effects of asphaltenes upon the crystallization behavior of a model waxy oil. Yield stress measurements on the model waxy oils with asphaltenes isolated from Shengli crude oil showed that both the relative amount of wax to asphaltenes and the aggregation state of the asphaltenes affected the crystallization properties of the wax. At very low asphaltene concentrations and high wax concentrations, the yield stress of the waxy gel is not significantly affected. At higher asphaltene concentrations, the asphaltenes significantly degraded the microscopic structure of the wax network and drastically reduced the yield stress. There is a threshold ratio of ∼100 paraffin/asphaltene molecules for such behavior. Asphaltenes produced large decreases in yield stress when they were highly aggregated. Oscillatory testing showed that in such cases asphaltene−asphaltene interactions contributed to the gel strength, in addition to the wax platelet interactions. Asphaltenes increased the wax precipitation temperature at high concentrations when large aggregates were present. However, at lower concentrations where the asphaltenes were less aggregated they suppressed precipitation. The aliphatic nature of the Shengli asphaltenes is an important determinant of the observed decrease in precipitation temperature and yield stress.