Effects of Nozzle L/D on Near-Field Development and Macroscopic Spray Characteristics of Common-Rail Diesel Sprays

Abstract

This study was performed to investigate the effects of L/D ratio of the nozzle on initial development and macroscopic spray behavior of diesel spray to understand the formation process of spray cone angle. Near-field and far-field spray visualization was performed for various injection pressures, and the effects of L/D ratio of the nozzle on spray cone angle were analyzed. A long-distance microscope and a CCD camera were used to obtain near-field spray images. Also, macroscopic spray development was evaluated using a high-speed camera and two metal halide lamps to compare the spray cone angle depending on L/D ratio. In the initial stage of injection, a laminar flow regime is observed, and downstream of the liquid column is deformed due to the large drag force of the surrounding gas. The area of the initial spray head, which has a small amount of momentum, becomes wider due to drag, and a strong eddy flow is formed around the deformed spray head. As the momentum of the supplied fuel increases over time, a mushroom-like structure is formed because momentum is continuously supplied at the center of the spray, while the outside of the spray head receives only drag force without providing additional momentum.