Application of Planar Doppler Velocimetry within Piston Engine Cylinders

The present article describes a method of obtaining the volumetric, steady state, isothermal velocity field of the in-cylinder flow by means of planar Doppler velocimetry (PDV, also known as Doppler global velocimetry, DGV). The results are used to validate CFD models as well as for the further computation of characteristic quantities such as the swirl and tumble numbers. The PDV-system used for the investigation is optimized for the measurement of time-averaged velocity data and utilizes three different light sheet directions and a single camera system to provide planar three-component velocity data of the cylindrical cross-section. By traversing the triple light sheet fixture along the cylinder axis (Z-axis), adjacent planes of velocity data are obtained from which the volumetric data set can be reconstructed (Fig. 1). Comparison between these measurements and those obtained through integral methods show very good agreement. Further, reproducibility measurements were carried out and indicate a mean measurement uncertainty of roughly ± 0.5 m/s. Tumble-numbers calculated from this data exhibit a mean variation of less than 1%. The described semi-automated PDV system has been qualified for routine measurements within the engine design cycle as well as for the inspection of production-specific manufacturing tolerances. Acquisition times for a data set as in Figure 1 is on the order of 5 minutes per valve setting (30 seconds per 2-D velocity map). Post-processing of the images is largely automated. Further steps toward full automation are under way. Fig. 1: Volumetric velocity map of stead-cylinder charge flow consisting of 8 separate measurement planes. Vectors represent the in-plane velocity components vx and vy, while the out-plane velocity component (vz) is given in colored contours. The cylinder head (and valves) is located at z=0. 1 1