A laser 2-focus velocimeter (L2F) was used for measurements of velocity and size of droplets in diesel fuel sprays. Diesel fuel was injected intermittently into the atmosphere using a 8-hole injector nozzle. The diameter of the nozzle orifice was 0.112mm. The rail pressure was set at 40MPa by using a common rail system. The period of injector solenoid energizing was set at 0.8ms to investigate the spray behavior under small valve opening. The L2F had a micro-scale probe which consists of two foci. The focal diameter was about 3μm, and the distance between two foci was 20μm. The data sampling rate of the L2F system was markedly high as 15MHz. L2F measurement was conducted at 10mm downstream from the nozzle exit. Temporal and spatial changes in the velocity and size of droplets inside sprays were investigated near the nozzle orifice and were correlated with the needle valve lift of the injector nozzle. Spray images were taken by using a 180ns spark light source, and temporal changes of the spray width were estimated. The spray was divided into two regions; the inner region and the periphery region. The results showed that temporal changes in droplet velocity at the spray center corresponded with the temporal changes in needle valve lift. The droplets’ Weber number in the inner region was larger than that in the periphery region of the spray. It was found that the turbulence intensity of droplet velocity was strongly correlated to the size of droplet in the inner region of the spray.
