CORRELATION BETWEEN LIGHT ABSORPTION SIGNALS OF CAVITATING NOZZLE FLOW WITHIN AND OUTSIDE OF THE HOLE OF A TRANSPARENT DIESEL INJECTION NOZZLE

The measurement technique presented relies on the large image magnification (46 times) of a real size transparent diesel injection nozzle (0.2 mm in diameter and 1mm in length). In the image plane two light fibres collect the light and guide it to two photomultipliers. The position of the measuring volumes relative to the nozzle in the object plane are then well defined and can be easily and freely chosen in the image plane. The cavitation bubbles in the nozzle serve as tracers since they are convected by the flow. The peak of the cross-correlation function between data windows from each measuring volume yields the delay of passage of structures from one measuring volume to the other. The distance between the measuring volumes is easy to measure in the image plane. The spatial resolution is sufficient to measure velocity profiles within the nozzle. The peak value of the correlation is also a measure of presence of cavitation in the jet when one measuring volume is placed within and one outside of the nozzle. The results show that cavitation collapse starts at the nozzle exit initiating atomization. NOTATION