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A laser 2-focus velocimeter (L2F) was used for measurements of velocity and size of droplets in diesel sprays. The L2F has a micro-scale probe which consists of two foci. Diesel fuel was injected intermittently into the atmosphere by using a 6-hole injector nozzle. The diameter of the nozzle orifice was 0.135mm. The injection pressure was set at 80MPa. Measurement positions were located at 5, 7, 10 and 15mm from the nozzle exit. The measurement result showed that the velocity of droplets at the spray center was the highest, and decreased in the direction towards the spray periphery. The size of droplets at the spray periphery was larger than the one at the spray center. The size of droplets decreased in the direction of droplet flight on the near nozzle plane. It is understood that the breakup of droplets occurred. The size of droplets increased in the direction of droplet flight at the spray periphery on downstream planes. It is understood that the coalescence of droplets occurred.

A laser 2-focus velocimeter (L2F) was used for measurements of velocity and size of droplets in diesel sprays. The L2F has a micro-scale probe which consists of two foci. The focal diameter is about 3 μm, and the distance between two foci is 18 μm. The data acquisition rate of the L2F was increased to 15 MHz in order to capture every droplet appearing in the measurement volume. Diesel fuel was injected intermittently into the atmosphere using a 5-hole injector nozzle. The diameter of the nozzle orifice was 0.113 mm. The injection pressure was set at 80 and 120 MPa by using a common rail system and the ambient pressure was varied from 0.1 to 3 MPa. The period of injector solenoid energizing was set at 3.0 ms. Droplets were evaluated in a period of 0.2 ms just after the spray tip passed the measurement position. Measurement positions were located at 6, 9 and 12 mm from the nozzle exit. The effect of ambient pressure on the droplet velocity in the near-nozzle region was unremarkable.