A laser 2-focus velocimeter (L2F) was used for the measurements of the velocity and size of droplets in diesel fuel sprays. The L2F had a micro-scale probe which consists of two foci. The focal diameter was about 3 µm, and the distance between two foci was 24 µm. 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, and the number of holes was 6. The injection pressure was set at 60 MPa, and the amounts of

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... l were set at 1.1 and 7.0 mg per injection. It was confirmed that the size of droplets near the nozzle under a smaller amount of injection was smaller than the one under a larger amount of injection. The droplet size decrease rate in the direction of spray injection was found to be larger at the spray upstream region compared to at the spray downstream region. There was a positive correlation between the droplet size decrease rate under a smaller amount of injection and the one under a larger amount of injection. The droplet breakup of diesel sprays was less dependent on the injection amount.