A comprehensive modeling study of in-cylinder fluid flows in a high-swirl, light-duty optical diesel engine

• Validation of CFD in-cylinder flows predictions in variable swirl optical engine.
• Ensemble average swirl, PIV velocities and vortex center well captured by RANS.
• Shortcomings of sector mesh modeling are analyzed.
• Model will help study turbulence, spray and ignition of PPC combustion strategies.

The effectiveness of computational fluid dynamics modeling as a tool for researching fuel-lean, low temperature engine combustion strategies relies on its capability to capture the local fluid flow properties that affect spray dynamics, mixture preparation and ignition kinetics. In this study, a comprehensive model of an optically accessible, single-cylinder light-duty diesel engine was developed for engine combustion research. The computational model includes the realistic combustion chamber and ducts geometries. Variable orientation throttles in the intake ducts were modeled to reproduce variable swirl generation. Full induction stroke calculations were run over a portfolio of intake swirl conditions, and validated against extensive measurements featuring global intake swirl ratios, in-cylinder particle image velocimetry (PIV)-measured velocity fields and swirl centers. The results showed good agreement with the experiments, and the model was used to understand the effects of different swirl generation strategies on the in-cylinder flow field. The implications of using simplified sector mesh geometries on the predictiveness of in-cylinder flow and turbulence quantities are described.