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Ongoing efforts in applying a “high-end” turbulent combustion model (a transported probability density function - tPDF - method) to direct-injection internal combustion engines are discussed. New numerical algorithm and physical modeling issues arise compared to more conventional modeling approaches. These include coupling between Eulerian finite-volume methods and Lagrangian Monte Carlo particle methods, liquid fuel spray/tPDF coupling, and heat transfer. Sensitivity studies are performed and quantitative comparisons are made between model results and experimental measurements in a diesel/PCCI engine. Marked differences are found between tPDF results that account explicitly for turbulence/chemistry interactions (TCI) and results obtained using models that do not account for TCI. Computed pressure and heat release profiles agree well with experimental measurements and respond correctly to variations in engine operating conditions.

Multidimensional computational fluid dynamics (CFD) has become an accepted and indispensible tool in the analysis and design of next-generation low-fuel-consumption, low-emissions internal combustion (IC) engines. Turbulent combustion models have been developed to deal with the wide variety of combustion phenomena that occur in spark- and compression-ignition, homogeneous- and stratified-charge engines. IC-engine combustion can vary from essentially premixed turbulent flame propagation, through turbulent-mixing-controlled nonpremixed combustion, to chemical-kinetics-controlled regimes, within a single device on a single engine cycle. In this review, an overview of the combustion systems of interest for reciprocating-piston IC engines is provided first. Then the underlying governing equations, and the manipulations and simplifications that lead to a tractable equation set suitable for engineering CFD calculations, are reviewed.

A comprehensive modeling and visualization study of flow and combustion is reported for a production four-valve-per-cylinder homogeneous-charge four-stroke-cycle spark-ignited engine. Coupled port and in-cylinder computations are presented for five combinations of valve deactivation, valve shrouding, and cam profile. Motored (induction and compression) results are compared with transient-water-analog flow-structure visualizations. A new flamelet model for homogeneous-charge turbulent premixed combustion has been implemented for fired engine simulations. Several issues in the application of CFD to flow and combustion modeling in practical port-and-cylinder systems are addressed. These include numerical inaccuracy, elucidation of the role of induction-generated flow structure and turbulence, and new insights into premixed flame propagation.