Assessment of LES-CMC Simulations for Spray A Combustion (original) (raw)
In the last decades, engine combustion research has focused on the understanding of the incylinder emissions mechanisms with the aim of their reduction. Supporting a variety of experimental diagnostics, extensive studies have been conducted using numerical tools in the RANS context, allowing for deeper insight into in-cylinder mean phenomena. However, due to the non-linear temperature dependence of chemical reactions and to the unsteady turbulent fluctuating nature of the flow field in spray applications, more complex numerical tools are needed for further advances in engine development. In this context, LES constitutes the current state-of-the-art, since it is able to resolve the large energy containing turbulent scales of motion and to predict a detailed instantaneous description of the mixing field. As a consequence it has seen successful application to study cycle-to-cycle variations as reviewed in . Despite recent progress, considerable challenges persist in accurately predicting turbulent reacting flows, since for many practical turbulent diffusion combustion applications with high Reynolds and Damkoehler numbers, molecular mixing and chemical reaction occur at the smallest dissipative scales [2], which are not resolved. Similar to RANS, LES therefore also requires advanced combustion models to account for turbulencechemistry interaction; the latter indeed has been observed to significantly affect combustion and emission formation . For non-premixed combustion, most modelling efforts are mixture fraction based, where the fluctuations of reacting scalars and temperature are correlated with those of the mixture fraction. It becomes clear that an accurate description of the flow field is of supreme importance, supporting even more the LES strategy.
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