Large Eddy Simulation of a Motored Single-Cylinder Engine Using System Simulation to Define Boundary Conditions: Methodology and Validation

Large Eddy Simulation (LES) appears today as a prospective tool for engine study. Even if recent works have demonstrated the feasibility of multi-cycle LES, they have also pointed out a lack of detailed experimental data for validation as well as for boundary condition definition. The acquisition of such experimental data would require dedicated experimental set-ups. Nevertheless, in future industrial applications, unconditional dedicated experimental set-ups will not be the main stream. To overcome this difficulty, a methodology is proposed using system simulation to define fluid boundary conditions (crankresolved intake/exhaust pressures and temperatures) and wall temperatures. The methodology combines system simulation for the whole experimental set-up and LES for the flow in the combustion chamber as well as a part of the intake and exhaust ducts. System simulation provides the crank-resolved temperature and pressure traces at the LES mesh inlet and outlet. LES results are compared to experimental measurements obtained on the corresponding optical single-cylinder engine under motored operation. For this purpose, statistical analysis over several consecutive LES engine cycles is performed to compare numerical results with Particle Image Velocimetry (PIV). The ability of the developed methodology to capture the in-cylinder cycle-to-cycle flow variations in a motored engine is demonstrated. This result points out the potential of LES to analyse cycle-to-cycle variations observed in sparkignition engines.