In-Cylinder Velocity Field Measurements in a Motored Diesel Engine

Measurements of three velocity components and of the corresponding turbulent fluctuations are reported obtained by laser Doppler anemometry in the cylinder of a FIAT-IVECO 8140 DI Diesel engine motored at 1000 rpm with a 16:1 compression ratio. The results show that the air swirl velocities at inlet valve closure are axially stratified while the intake-generated axial flow structures persist, although decaying, up to 70° BTDC when the squish effect transforms the in-cylinder flow structure. The presence of a flow towards the piston crevice is detected at 20° BTDC while at TDC of compression the formation of at least, one toroidal vortex in the axial plane inside the piston bowl is detected. The findings of this investigation are compared with similar measurements in simplified engine configurations and reveal a satisfactory qualitative as well as quantitative agreement.