Visualization Engine Research Articles

A displaced-line velocity diagnostic and its application in a visualization engine

A technique for measuring three-dimensional velocity by imaging the displacement of a marked fluid line is described, together with its use in an automotive visualization engine. In a flow seeded with 2–3 μ phosphorescing particles, a line is excited by a UV laser beam, deformed by the local velocity field, and detected by stereo low-light-level video cameras. The derivation of velocity from digitized images is discussed and capabilities of the diagnostic are assessed. Some image data taken in the engine are shown and quantitative two-component velocity plots along the line are presented.

Thermal boundary layer thickness in the cylinder of a spark-ignition engine

The thicknesses of the thermal boundary layers in the cylinder of a spark-ignition engine were measured throughout the complete operating cycle. The engine used for these experiments was a special visualization engine with a square cross-section ‘cylinder’ and two quartz glass walls. Measurements of thickness were taken at different locations, speeds and loads, from schlieren photographs. The results show that the layers on the cylinder wall reach a maximum thickness of about 2 mm at the end of expansion. On the cylinder head and piston top, the layers are two to three times thicker. Reducing engine speed resulted in thicker layers, while changing load showed no significant effects on thickness. It is shown that on the cylinder wall, the thermal boundary layer thickness depends on thermal diffusivity and the time available for the layer to develop. The growth of this layer was correlated with an expression in the form δ T √( αt) ∞ Re 0.2.