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In recent years, Large Eddy Simulation (LES) has been successfully applied to non-premixed and premixed turbulent combustion problems [1,2,3]. In most technical combustion applications, the pure non-premixed or premixed combustion models are no longer valid, since partially premixed combustion has to be taken into account. An example is the stabilization region of a lifted non-premixed flame. To overcome this problem, a Combined Conserved Scalar/Level-Set Flamelet model has been proposed [4,5], which allows for the computation of reactive flows, where both premixed and non-premixed combustion occurs. In this formulation, the G-equation method is used to describe partially premixed flame propagation and to distinguish between burned and unburned regions. The reacting gases in the post-flame region are described by a laminar diffusion flamelet approach. The principal roadmap for the further development and validation of these models is to develop and validate the appropriate methods for the pure premixed and non-premixed combustion situations, and combine the resulting models for a more general formulation. Much of this work has been done in the past. We have developed unsteady flamelet models for LES of non-premixed turbulent combustion [1,2], and a level-set method for LES of premixed turbulent combustion [3]. These models have been validated with premixed and non-premixed turbulent jet flame experiments. Preliminary simulations with a Combined Conserved Scalar/Level-Set Flamelet Model have already been performed [6,5]. Results from these simulations are shown in Figs. 1 and 2. Recently, we have developed a new consistent formu-

The development of surrogate mixtures that represent gasoline combustion behavior is reviewed.1 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.

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The Lagrangian Flamelet Model is formulated as a combustion model for large-eddy simulations of turbulent jet diffusion flames. The model is applied in a large-eddy simulation of a piloted partially premixed methane/air diffusion flame (Sandia flame D). The results of the simulation are compared to experimental data of the mean and RMS of the axial velocity and the mixture fraction and the unconditional and conditional averages of temperature and various species mass fractions, including CO and NO. All quantities are in good agreement with the experiments. The results indicate in accordance with experimental findings that regions of high strain appear in layer like structures, which are directed inwards and tend to align with the reaction zone, where the turbulence is fully developed. The analysis of the conditional temperature and mass fractions reveals a strong influence of the partial premixing of the fuel.