Effects of injector valve movement on diesel spray characteristics under short full valve opening

A laser 2-focus velocimeter (L2F) was used for the measurement of diesel fuel sprays. Temporal and spatial changes in the number, 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. The L2F had a micro-scale probe which consists of two foci. The focal diameter was about 3 mu m, and the distance between two foci was 17 mu m. The data sampling rate of the L2F system was markedly high as 15MHz. Fuel sprays were injected intermittently into the atmosphere by using a common rail injector. The orifice diameter of the injector nozzle was 0.112mm and the rail pressure was 40MPa. The periods of solenoid energizing was set at 2.0ms. Measurement positions were located at 10mm downstream from the exit of the nozzle orifice. The results show that droplets mainly existed in the region off the spray center in the early injection period and concentrated at the spray center in the middle of injection period. Temporal changes in the number of droplets near the spray center were strongly affected by the needle lift and there in the relatively wide region were affected by the injection rate. Temporal changes in the droplet velocity near the spray center were strongly affected by the injection rate. The luminance distribution of the spray image was similar to the distribution of the number of droplets multiplied by the square of droplet size.