Quantitative Comparisons of Macroscopic Characteristics of a Flash-Boiling Spray and a Turbulent Round Jet

In order to quantitatively investigate the macroscopic characteristics of flash-boiling atomization, the spray injected through a plain-orifice nozzle under atmospheric conditions was directly imaged and analyzed by the multi-threshold algorithm. The spray images were acquired at various times after the start of actuation using a high-speed visualization system. The light intensity level of images implies the local relative mass concentration of droplets in the spray. Transient contour plots of spray images at various thresholds were analyzed and compared with turbulent round jets of diesel. A new term, transient continuous cone angle, was defined to characterize the flash-boiling spray. The relative mass concentration distributions and continuous cone angles of the sprays during the start, development and end periods of the atomization were discussed for two different sprays. The grayscale levels of sprays in the outer and end regions of the sprays were lower compared to those in the center regions, because the droplets at the outer and end regions were well-atomized by the volatile nature of the material and the friction between the injected droplets and the surrounding gas. The continuous spray cone angle showed a significant variation in the expansion region of the spray, and it provides a new technique for automatic spray structure analysis.