Experiments and Large-Eddy Simulation for a Flowbench Configuration of the Darmstadt Optical Engine Geometry

The development and control of spark-ignition engines with increased efficiency and reduced engine-out emissions requires tools and methods capable of providing insight and eventually predicting Cycle-to-Cycle Variations (CCV). To this end, Large-Eddy Simulations (LES) can improve the understanding of stochastic in-cylinder phenomena during the engine design process. However, available LES methods are typically not able to reproduce the full extent of cyclic variability observed in experiments, and computational costs are higher compared to established simulation approaches. In this work, an engine flowbench configuration suitable for validation of LES methods and intake flow assessment is considered. To supplement an existing validation database, Particle Image Velocimetry (PIV) and wall pressure measurements have been conducted in a reference optical engine geometry, which is available through the Darmstadt Engine Workshop. To facilitate future LES validation studies, a simulation model is proposed. LES predictions computed with an in-house code match the experimental data reasonably well. Analysis of the mean in-cylinder flow field shows that the stagnation flow caused by the interacting valve jets counteracts the formation of a bulk tumble vortex structure near the center plane. By using Proper Orthogonal Decomposition (POD), two distinct flow features that govern the intake jet dynamics are identified. More work is required to rigorously assess bulk tumble vortex stability and the impact on CCV.