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An advanced laser 2-focus velocimeter (L2F) has been applied to the measurement of droplet velocities and sizes in a dense region of diesel fuel spray. The maximum rate of data sampling of the L2F was set at 15 MHz. The fuel was injected into the atmosphere by using a common rail injector. The rail pressure was set at 40 and 70 MPa. The nozzle hole diameter of the injector was 0.113 mm. The L2F can detect droplets just after the spray tip reaches the measurement position 30 mm downstream from the nozzle. The result of the measurement shows that the higher injection pressure leads the higher droplet velocity in the core of the spray. It is clearly shown that the smaller droplets after active disintegration are dispersed spatially under higher injection pressure.

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.

In order to get fundamental information about the droplet disintegration in the core region of diesel fuel spray, an advanced laser 2-focus velocimeter (L2F) was used for the measurements of velocity and size of droplets. The L2F with micro-scale probe has high optical SN ratio and high spatial resolution. Measured was the fuel spray injected into the atmosphere intermittently from a single hole nozzle. The diameter of the orifice was 0.2 mm. Measurements were conducted on four planes where the axial distances were 10, 20, 30, and 40 mm respectively downstream from the orifice exit. As the injection pressure and needle valve lift change unsteadily in case of the intermittent injection spray, time change of spatial distributions of velocity and size was measured and time change of the joint probability density associated with velocity and size was examined.

A laser 2-focus velocimeter (L2F) has been applied for the measurements of velocity and size of droplets in the core region of diesel spray. The L2F had a micro-scale probe which consists of two foci. The distance between two foci was 14 μm and the focus size was nominally 3 μm. Valid data were extracted by the criteria that a downstream signal was sequentially observed after an upstream signal. The maximum data sampling rate of the L2F was set at 15 MHz. Fuel was intermittently injected into the atmosphere by using a common rail injector. The nozzle orifice diameter of the injector was 0.113 mm and the injection pressure was set at 70 MPa. Five measurement positions were located in the plane of 15 mm from the nozzle orifice. The L2F could detect droplets just after the spray tip reached the measurement position. Measurement result showed that the velocity and size of droplets in the spray core decreased at the off-axis region.

A laser 2–focus velocimeter (L2F) has been applied for the measurements of velocity and size of droplets in the core region of diesel spray. The L2F had a micro–scale probe which consists of two foci. The distance between two foci was 14 µm and the focus size was nominally 3 µm. Valid data were extracted by the criteria that a downstream signal was sequentially observed after an upstream signal. The maximum data sampling rate of the L2F was set at 15 MHz. Fuel was intermittently injected into the atmosphere by using a common rail injector. The nozzle orifice diameter of the injector was 0.113 mm and the injection pressure was set at 70 MPa. Five measurement positions were located in the plane of 15 mm from the nozzle orifice. The L2F could detect droplets just after the spray tip reached the measurement position. Measurement result showed that the velocity and size of droplets in the spray core decreased at the off–axis region.