Measurements of velocity and size of droplets in core region of diesel spray from common rail injector using micro-probe L2F

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 has a micro-scale probe which consists of two foci. The focal diameter is about 2 μm, and the distance between two foci is 20 μm. The feature of this L2F is that the focus is reduced to near the diffraction limit. Investigated was the fuel spray injected into the atmosphere intermittently from a 5-hole injector nozzle with the orifice diameter of 0.16 mm. The injection pressure was set at 100 MPa by using a common rail system. Measurements were conducted on the plane where the axial distance was 20 mm from the orifice exit. Valid data were extracted by a conditional sampling method based on the fact that a droplet passes through both the upstream and downstream focus. Valid data was only about 30% of the acquired data in the injection period because the number density was so high. The velocity and size of droplets showed the highest value at the spray center and decreased at off-axis positions. It is clearly seen that the velocity and size has a nearly uniform distribution at first half of injection period, and varies spatially at later half of injection period.