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Computational fluid dynamic (CFD) simulations that include realistic combustion/emissions chemistry hold the promise of significantly shortening the development time for advanced high-efficiency, low-emission engines. However, significant challenges must be overcome to realize this potential. This paper discusses these challenges in the context of diesel combustion and outlines a technical program based on the use of surrogate fuels that sufficiently emulate the chemical complexity inherent in conventional diesel fuel.

The development of surrogate mixtures that represent gasoline combustion behavior is reviewed. Combustion chemistry behavioral targets that a surrogate should accurately reproduce, particularly for emulating homogeneous charge compression ignition (HCCI) operation, are carefully identified. Both short and long term research needs to support development of more robust surrogate fuel compositions are described. Candidate component species are identified and the status of present chemical kinetic models for these components and their interactions are discussed. Recommendations are made for the initial components to be included in gasoline surrogates for near term development. Components that can be added to refine predictions and to include additional behavioral targets are identified as well. Thermodynamic, thermochemical and transport properties that require further investigation are discussed.

Auto-ignition in Diesel engines, occurring essentially under non-premixed and partially premixed conditions, is considerably different to homogeneous ignition. In order to study the relevant chemistry--mixing interactions, it is assumed that the ignition of Diesel fuel can be described by using the single component model fuel n-heptane. Starting from a detailed chemical reaction scheme with about 1000 elementary reactions among 168 chemical components, a skeletal mechanism consisting of 98 reactions and 40 components is derived, which is still capable of describing the auto-ignition process under Diesel engine conditions and concentrations of NO, relevant intermediate components. Introducing steady state assumptions for intermediate species which are consumed rapidly leads to a reduced 14-step mechanism. The mechanism is validated with auto-ignition delay times from shock tube experiments by Adomeit for different temperatures, pressures, and equivalence ratios.

In this work, surrogate fuels composed of n-decane and alpha-methylnaphthalene (AMNL) with different compositions according to the reference cetane numbers 53, 45, 38, and 23 are investigated. In addition to the two-component mixtures, we examine a three-component mixture composed of n-decane, AMNL, and di-n-butyl ether (DNBE) corresponding to a reference cetane number of 53. Spray characteristics of liquid and fuel vapor phase and the relationship between ignition quality and lift-off length are investigated. The experimental results show, first of all, that for these mixtures, the cetane number is a good indicator for the ignition delay. Diesel and surrogate fuels have different liquid penetration lengths, which depend on the evaporation rate, and hence vapor pressure and boiling point of the fuels.

In order to deeply investigate and improve the complete path from biofuel production to combustion, the cluster of excellence “Tailor-Made Fuels from Biomass” was installed at RWTH Aachen University in 2007. Recently, new pathways have been discovered to synthesize octanol [1] and di-n-butylether (DNBE). These molecules are identical in the number of included hydrogen, oxygen and carbon atoms, but differ in the molecular structure: for octanol, the oxygen atom is at the end of the molecule, whereas for DNBE it is located in the middle. In this paper the utilization of octanol and DNBE in a state-of-the-art single cylinder diesel research engine will be discussed. The major interest has been on engine emissions (NOx, PM, HC, CO, noise) compared to conventional diesel fuel.