We analyzed the in-cylinder flow fields of an optical-access single cylinder diesel engine with the PIV and STAR-CD CFD code. The PIV analysis was carried out in the bottom and side view mode during a compression stroke (ATDC 220°-340°) at 600 rpm. The flow pattern traced by the streamlines, the location of vortex center, the generation and disappearance of tumble, and the squish effect agreed well, as visualized by the PIV and CFD.
Vorticity and spatial fluctuation intensities abruptly increased from ATDC 310, reflecting more complicated flow pattern as approaching TDC. In a quantitative sense, the velocity magnitudes obtained from the PIV were, on an average, higher than those from the CFD by 1 m/s approximately and the difference in velocity magnitude between them was about 26 %.
In the CFD analysis, the standard high Reynolds κ-ε and RNG k-ε model were adopted for calculation with tetra and hexa or their hybrid meshes, to determine the turbulence model dependencies.
Among various combinations of such CFD schemes, the standard high Reynolds k-ε model was proven most suitable for “low engine speed” condition as in this study.