Multi-Cycle LES Simulations of Flow and Combustion in a PFI SI 4-Valve Production Engine

The LES technique has been applied to the simulation of 9 consecutive complete engine cycles of a single cylinder, spark-ignited 4valve engine. The simulations have been realized with the AVBP code, jointly developed by IFP and CERFACS. An extended coherent flame model approach (ECFM-LES) has been used to model spark ignition and turbulent combustion, and is shortly presented, along with the used turbulence models. The engine was fuelled with gaseous propane injected far upstream from the intake, so that fuel injection was not simulated, the fresh charge being assumed to be homogeneous. After a description of the numerical set-up, results obtained with LES are compared with experimental findings on cycle to cycle cylinder pressure evolutions. It is shown that LES indeed captures qualitatively the observed cyclic variability of the engine, even with only 9 cycles simulated. An analysis of the LES results demonstrates the unprecedented possibility this technique offers for understanding the occurrence of cycle to cycle variations.