Towards large eddy simulation of combustion in spark ignition engines

Internal combustion engine simulations are commonly performed using the RANS (Reynolds averaged Navier–Stokes) approach. It gives a correct estimates of global quantities but is by nature not adapted to describe phenomena strongly linked to cyclic variations. On the other hand, large eddy simulation (LES) is a promising technique to determine successive engine cycles. This work demonstrates the feasibility of LES engine cycles simulation by using a flame surface density (FSD) approach. This approach, presented in a first section, combines an Eulerian spark ignition model derived from the RANS AKTIM model [J.M. Duclos, O. Colin, Arc and Kernel Tracking Ignition Model for 3D SI Engines Calculations, Comodia, Nagoya, Japan, 2001, pp. 343–350] and a Coherent Flame Model (CFM) [S. Candel, T. Poinsot, Combust. Sci. Tech. 70 (1990) 1–15; O. Colin, A. Benkenida, C. Angelberger, Oil & Gas Sci. Techn.—Rev. IFP 58 (1) (2003) 47–32] describing the flame propagation. The CFM model, commonly used in RANS simulations, is here formulated in a LES context. In a second part, the whole ignition-combustion model is validated against an experiment relative to the turbulent ignition and flame propagation of a stoichiometric propane-air mixture [B. Renou, A. Boukhalfa, Combust. Sci. Tech. 162 (2001) 347–371]. Finally, LES engine cycles simulations are performed on a real engine configuration. First, the sensitivity of the model to the LES combustion filter size ^D is examined, showing a weak dependence of the modelling approach to D. Then results are compared to those obtained with the algebraic model for the FSD proposed by Boger et al. [M. Boger, D. Veynante, H. Boughanem, A. Trouve´, Proc. Combust. Inst. 27 (1998) 917–925] and the need for non-equilibrium combustion models is demonstrated