Analysis of a Diesel Spray Using a Mechanical Slicing Device

This paper gives a summary of image velocimetry measurements performed in a sliced diesel spray. The slicing of the spray was necessary to achieve sufficient image quality in the more dense regions of the spray. The images were double exposed to allow auto-correlation based velocimetry. The illumination was achieved with a xenon flashlight behind the spray and consequently the droplets were visible as dark shadows.

Images were acquired from different points downstream from the nozzle, and a number of different radii were employed at every position. In the images the smaller droplets seem to be spherical, while the larger ones are distorted due to high weber numbers. Computer simulations indicate that large droplets may reach high weber numbers when passing through the slit, and that some of these large droplets break up. Simulations were also used to estimate how much the velocity of the droplets was affected by the slicing device, and accordingly the expected reduction in velocity does not exceed 30 % for the smallest droplets. Considering this, an acceptable agreement was found between velocities measured with the slicing device and velocity data found in the literature. Therefore, it is concluded that the slicing device used in this paper gives new valuable information about the internal structures in dense diesel sprays.