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In previous publications, Singh et al. [1, 2] have shown that direct integration of CFD with a detailed chemistry auto-ignition model (KIVA-CHEMKIN) performs reasonably well for predicting combustion, emissions, and flame structure for stratified diesel engine operation. In this publication, it is shown that the same model fails to predict combustion for partially premixed dual-fuel engines. In general, models that account for chemistry alone, greatly under-predict cylinder pressure. This is shown to be due to the inability of such models to simulate a propagating flame, which is the major source of heat release in partially premixed dual-fuel engines, under certain operating conditions. To extend the range of the existing model, a level-set-based, hybrid, auto-ignition/flame-propagation (KIVA-CHEMKIN-G) model is proposed, validated and applied for both stratified diesel engine and partially premixed dual-fuel engine operation.

Three different approaches for modeling diesel engine combustion are compared against cylinder pressure, NOx emissions, high-speed soot luminosity imaging, and 2-color thermometry data from a heavy-duty DI diesel engine. A characteristic time combustion (KIVA-CTC) model, a representative interactive flamelet (KIVA-RIF) model, and direct integration using detailed chemistry (KIVA-CHEMKIN) were integrated into the same version of the KIVA-3v computer code. In this way, the computer code provides a common platform for comparing various combustion models. Five different engine operating strategies that are representative of several different combustion regimes were explored in the experiments and model simulations. Two of the strategies produce high-temperature combustion with different ignition delays, while the other three use dilution to achieve low-temperature combustion (LTC), with early, late, or multiple injections.