Measurement and Modeling of the Flow-Field in a DI Diesel Engine: Effects of Piston Bowl Shape and Engine Speed

The flow-field of an automotive DI Diesel engine is characterized by experiments in a motored engine using Laser Doppler Velocimetry and by CFD simulations. Only one cylinder is active and a specific swirling intake duct is used. Various bowls with different shapes are investigated: fiat or W-shaped bowls, with or without re-entrant. The influence of engine speed is also studied.

The mean velocity and turbulence evolutions are measured with back-scatter LDV experiments using an optical access in an extended piston.

The simulations are performed using the KMB code, a modified version of KIVA-II. Along with the detailed flow-field description, integral quantities characterizing the flow are derived.

The comparison between LDV data and CFD results is shown to be satisfactory. The effects of geometry and engine speed on spatial profiles and temporal evolution of mean and turbulent velocities are correctly reproduced. This investigation has allowed a better understanding of the piston bowl shape effects on the combustion chamber flow. Among these effects, the role of the re-entrant in the W-shaped bowls is shown to increase both swirl number and turbulence level around TDC.