Spray Structure and Associated Droplet Velocity in the Initial Stage of Diesel Fuel Injection

This paper reports an experimental study of hith-pressue diesel fuel sprays in their initial stage of development. Diesel fuel is injected from a single-hole nozzle at an injection pressure of 50 MPa into a high-pressure vessel. The internal structure of the spray is visualized with a laser-induce fluorescence (LIF) method. A direct cross-correlation PIV technique is applied to the spray images acquired with a double-pulsed illumination system in order to measure the droplet velocity distributions in the intial stage of spray development. It is found that some droplets located slightly upstream of the spray tip can have substantially higher axial velocities than the droplets located on the spray tip. It is also found that some droplets near the spray tip have large radial velocities as if they are injected out of the spray core. These findings ae discussed in detail in conjunction with possible mechanisms for the generation of large-structures of diesel fuel sprays.