Evaluation of the unsteady flamelet progress variable approach in Large Eddy Simulations of the ECN Spray A

Abstract

Within the Unsteady Flamelet Progress Variable - Large Eddy Simulation (UFPV-LES) approach the local scalar dissipation rate represents one key parameter, significantly affecting the ignition behaviour. In this study, the UFPV-LES approach is evaluated for ECN Spray A baseline conditions, relevant for diesel engines. After confirming its general applicability, using experimental data under non-reacting and reacting conditions, special attention is paid to the distribution of the local scalar dissipation rate. Based on the findings of this analysis, a reduced modeling approach, considering only igniting flamelets starting from the adiabatic mixing line between the fuel and oxidizer, is investigated. The performance of this reduced approach is assessed systematically, using the UFPV-LES results as a reference. Based on an a-priori analysis, regions affected by the model reduction are identified and evaluated. A subsequent evaluation in an a-posteriori analysis, i.e. a coupled LES, reveals similar results in terms of local flame structure as well as global ignition characteristics and confirms the applicability of the reduced model under the ECN Spray A baseline conditions.