Molecular
Tagging Velocimetry (MTV) is used to measure the in-cylinder fluid motion of an
internal combustion engine. MTV is a non-intrusive optical technique for
measuring the flow in a plane. This
technique, which was developed here at Michigan State University, is superior to
Laser Doppler Velocimentry (LDV) since the flow is seeded with molecules as opposed to particles so there is
no question as to whether the particles actually follow the flow.
These molecules have the property of fluorescing when excited by UV
light, then continuing to phosphoresce for some time after the UV light is
removed. In MTV, the tracer molecule
is "tagged" by the pulse of a UV laser by way of two sets of
intersecting lines forming a grid and an image (see Figure 1) is taken of
the fluoresce with an intensified CCD camera.
This is done several times and the images are averaged to obtain a
reference image. Then the process
is repeated, but this time the image is recorded after the laser pulse, but
still within the phosphorescence lifetime of the molecules (see Figure 2).
The time between images is known and the distance each line intersection
has traveled with the flow and can be measured giving a velocity vector for each
intersection point. With this technique, several quantities including vorticity,
circulation, and cycle-to-cycle variability can be determined.
