Application of a flamelet-based CFD combustion model to the LES simulation of a diesel-like reacting spray

Abstract

Spray A from ECN, representative of diesel-like sprays, is modelled in the frame of Large-Eddy Simulations (LES) with a Dynamic Structure (DS) turbulence model in conjunction with an Unsteady Flamelet Progress Variable (UFPV) combustion model. In this work, the spray flow field is first calibrated under inert conditions against experimental data. In a second step, the reactive spray is simulated in order to describe the flame internal structure when varying ambient temperature. The model shows a good agreement with experimental results and describes the trends observed in flame global parameters, such as ignition delay (ID) and lift-off length (LOL). Low fluctuations are observed in LOL positioning revealing an intense chemical activity at the height of the base of the flame, which stabilizes the reaction in spite of the turbulent fluctuations. The analysis of the LES instantaneous fields shows how ignition kernels appear upstream of the base of the flame, clearly detached from the reaction zone, and grow and merge with the main flame in agreement with previous reported experimental and modelling results. The ambient temperature has a clear impact on the flame structure described by the model and the whole set of results reveal that in the frame of LES simulations the UFPV model is suitable for the calculation of diesel flames.