 |
A laser 2-focus velocimeter (L2F) was used for the measurements of the velocity and size of droplets in diesel fuel sprays injected from a solenoid type diesel injector. The L2F had a micro-scale probe which consists of two foci. The focal diameter was about 3 micro meters, and the distance between two foci was 20 micro meters. The fuel was stored once in a common rail and was injected intermittently to the atmosphere. The diameter of the nozzle orifice was 0.15 mm. The injection pressure was changed from 60 to 100 MPa, and the boost current of the injector needle opening was changed from 9 to 19A. The spray image was taken by a CMOS camera with 1.62 million pixels and a xenon lamp with 180 ns lighting. The spray width was evaluated by the spatial distribution of brightness at 10 mm downstream from the nozzle exit. The spray widths were large at the early and final stage of injection under all the boost current conditions. As the boost current became larger, the time when the spray width was the largest became earlier. The effects of boost current on the maximum of spray width at the early stage and on the spray width at middle stage were small. The L2F measurement was conducted at the spray center, 10 mm downstream from the nozzle exit. The velocity of droplet increased with the time at early stage under all the boost current conditions. As the boost current became larger, the time when the droplets of spray tip observed at the measurement position of L2F became earlier. This reason was thought that the needle opening speed became higher due to the increase of the boost current. At the early stage, the size of droplets under the condition of large boost current was larger than the one under the condition of low boost current. It was thought that the stage of seat contraction was shortened and that the turbulence inside the nozzle was decreased. The effects of boost current on the spray characteristics was large especially at the early period of injection.
