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To enable the modeling of modern diesel engines, this work furthers the development of multi-dimensional flamelet models for application to designs that employ multiple injection strategies. First, the flamelet equations are extended to two dimensions following the work of Hasse and Peters [1] and Doran et al. [2] and a method of coupling the resulting equations interactively to a turbulent flow simulation for use in unsteady calculations is described. The external parameters required to solve the flamelet equations are the scalar dissipation rates. In previous studies, the dissipation rates of each mixture fraction have been scaled according to their realizable bounds and the cross-dissipation rate between mixture fractions has been neglected.

A general model framework for investigating various injection strategies in compression ignition engines with both mixture and thermal inhomogeneities is presented using an extended representative interactive flamelet model. The equations describing evolution of chemistry are written for a scalar phase space of either one or two dimensions and an approach for modeling multiple injections is given. The combustion model is solved interactively with the turbulent flow field by coupling with a Reynolds-Averaged Navier-Stokes (RANS) solver. The model is applied in the simulation of a split-injection diesel engine and results are compared to experimental data obtained from a single cylinder research engine.

Strict NOx and soot emission regulations for Diesel engines have created an interest in low-temperature partially-homogeneous combustion regimes in both the US and Europe. One strategy, Homogeneous-Charge Late-Injection (HCLI) combustion utilizes 55% or more cooled external Exhaust Gas Recirculation (EGR) with a single Direct Injection strategy to control ignition timing. These engines are operated at low temperatures to ensure near zero NOx emissions, implying that fuel in the thermal boundary layers will not reach sufficient temperature to fully oxidize, resulting in Unburnt Hydrocarbon (UHC) and CO emissions. Of particular interest to HCLI engines are the UHC's that are not fully oxidized by the Diesel Oxidation Catalyst (DOC). Experimental measurements reveal that at average equivalence ratios greater than 0.8, methane is the single largest tailpipe-out UHC emission.

Homogeneous-Charge Compression Ignition (HCCI) engines have been shown to have higher thermal efficiencies and lower NOx and soot emissions than Spark Ignition engines. However, HCCI engines experience high levels of carbon monoxide (CO) and unburnt hydrocarbon (UHC) emissions. These pollutants are formed in regions of the cylinder where wall heat loss is significant. Improving CO and UHC emissions in HCCI engines requires a fundamental understanding of the heat loss, chemical kinetics, and transport between near wall regions and regions less affected by heat loss. In this study an enthalpy-based flamelet approach is introduced and applied in a simulation of a Rapid Compression Machine operated under HCCI conditions. This approach directly models transport between regions of higher and lower enthalpies. Results are compared to experimental data from Murase and Hanada [6]. The simulations correctly predict ignition timing trends as a function of initial mixture temperature.