  The focus of this work is to demonstrate how spatially resolved image
information from diesel fuel injection events can be obtained using a
forward-scatter imaging geometry, and used to calculate the velocities of
liquid structures on the periphery of the spray. In order to obtain accurate
velocities directly from individual diesel spray structures, those features
need to be spatially resolved in the measurement. The distributed structures
measured in a direct shadowgraphy arrangement cannot be reliably analyzed for
this kind of velocity information. However, by utilizing an intense collimated
light source and adding imaging optics which modify the signal collection,
spatially resolved optical information can be retrieved from spray edge regions
within a chosen object plane. This work discusses a set of measurements where a
diesel spray is illuminated in rapid succession by two ultrafast laser pulses
generated by a mode-locked Ti-Sapphire oscillator seeding a matched pair of
regenerative amplifiers. Light from the object plane, located at the center of
the spray, is directed by a set of imaging optics to the detection plane, where
it forms a shadow image on the face of a frame-transfer CCD. In this
configuration the depth-of-field of the imaging optics limit detected light,
effectively increasing the efficiency of signal collection within the object
plane and suppressing out-of-focus contributions. Time-correlated images are
collected in this manner and analyzed to obtain object plane velocity data for
in-focus edge features of the spray.
