Recent progress in the development of diesel surrogate fuels William Pitz, Charles Mueller ME 769 Presentation Sihan Jin 02/19/2015

Overview Chemical kinetic models for diesel fuel components (n-Alkanes, iso-Alkanes, Cycloalkanes, etc.) Surrogate mixtures Reduction of chemical kinetic mechanisms Selection of surrogate mixtures Physical properties Recommendations Summary

Chemical kinetic models for diesel fuel components Petroleum-based diesel fuel is primarily comprised of n-alkanes, iso-alkanes, cycloalkanes and aromatics. The carbon number of the components range from approximately C10-C22. An average carbon number is 14 or 15.

Chemical kinetic models for diesel fuel components n-Alkanes Chemical kinetic detailed mechanisms for n-Alkanes from n-C8 up to n-C16 have been developed. With previous work, this allows simulation of all n-alkanes up to C16. Cycloalkanes Detailed chemical kinetic models for the oxidation of cyclohexane have been developed. These models generally reproduce well the oxidation of cyclohexane under conditions in a stirred reactor and a rapid compression machine (RCM). Aromatics Aromatics comprise a large fraction of diesel. Development in chemical kinetic modeling and experimental investigation of alkyl substituted benzenes, naphthalenes and tetralin has been made in recent years.

Surrogate mixtures Surrogate mixtures are mixtures of components used to represent the target, real fuel whose behavior one desires to model. Lemaire et al. have investigated the IDEA surrogate diesel fuel which consist of 70% n-decane and 30% 1-methylnaphthalene(1-MN) and compared it to a low-sulfur diesel.

Reduction of chemical kinetic mechanisms The most obvious way to reduce computational cost is to reduce the number of species and reactions in the mechanism, while maintaining accuracy. Lu and Law have developed a directed-relational graph (DRG) method for mechanism reduction and stiffness removal for further computational cost reduction.

Selection of surrogate mixtures Once a palette of surrogate compounds is available, we need to select the surrogate compounds and their amount that will be included in a surrogate fuel. Various procedures have been examined and discussed so far. Zhang et al. matched chemical composition of a surrogate fuel to the target practical fuels by using nuclear magnetic resonance (NMR) analysis. Colket et al. discussed the combustion and physical properties that are important to match between a surrogate fuel and a target fuel. Dryer et al. advocated matching C/H ratio, threshold sooting index (TSI) and cetane number in surrogate fuel and target jet fuel.

Physical properties When experiments are performed, the physical properties of the diesel surrogate fuel need to match those of the target fuel so that their injection, vaporization and mixing characteristics are similar. Holley et al. proposed transport properties for n-alkanes and 1-alkenes based on correlations of corresponding states. Bruno et al. have developed an approach called the advanced distillation curve (ADC) for measuring distillation curves for practical fuels that measures the true thermodynamic state of the fuel. Huber et al. developed a surrogate mixture model to represent the physical properties of a coal-derived liquid fuel.

Recommendations High purity sources of iso-alkanes, cyclo-alkanes, aromatics and tetralins Data required for compounds with higher molecular weight as well as molecular structures. Comparison between data acquired using target fuels and those obtained at the same conditions using corresponding surrogate fuels to avoid high cost. Fundamental physical and transport property data for each of the pure compound. Controlled measurements should be made with the surrogate fuel and the results should be compared with CFD results.

Summary Significant progress has been made in all the fuel classes of iso-alkanes, cycloalkanes and aromatics. Significant progress has been made on new mechanism reduction methods. Fundamental experimental data is needed to fill out the higher carbon range of diesel fuel. A considerable gap in the work on the iso-alkane chemical class. A lack of work on surrogate fuels that have components to represent the high molecular weight end of diesel.