Application of Particle Tracking Velocimetry to the Cyclic Variability of the Pre-Combustion Flow Field in a Motored Axisymmetric Engine

A particle tracking velocimetry (PTV) system has been developed to measure two dimensional velocity fields in a motored axisymmetric engine with a transparent cylinder. The intake flow was seeded with phenolic microballoons (40 μm hollow spheres) and illuminated by a 1 mm thick horizontal sheet of pulsed laser light from a 25 Watt copper vapor laser capable of 30 ns pulses. Photographs containing tracks of dots representing the multiply exposed path of each particle were produced. These images were digitized by a custom scanner capable of 3456 by 5184 pixel resolution and binarized using an iterative threshold routine in order to locate the particles. Software then determined how the individual particles are organized into tracks and presented the results for operator verification. Velocity magnitude and direction were computed for each track and the results were interpolated to a fixed grid for further analysis. Cases of 50 realizations each were run at TDC compression for various operating conditions (swirl speed, valve lift) and the distribution of various scalar parameters of the flow (swirl center location, velocity at origin, swirl center spacing) were computed in order to quantify the repeatability of the flow.