Abstract
Keywords
Depth of Field Effects, Laser Sheet Imaging, LIF (Laser-Induce Fluorescence) Imaging, Pre-Swirl Spray
Abstract
The depth of field effects in the laser sheet imaging was considered for the droplet sizing of the pre-swirl spray, which is formed before the hollow-cone type main-swirl spray from a D.I. gasoline injector, and which shows the high transient characteristics and axial velocity. In addition, a microscopic imaging technique was applied to get the spatially high-resolution LIF tomograms of the pre-swirl spray. The Nd:YAG laser sheet with 1 mm thick was used as a light source to make the LIF tomograms that was imaged using a high-resolution CCD camera. The image processing technique was applied to determine the droplet size. In the image processing procedure, the laser sheet-straddling large-sized droplets were carefully taken into account to remove the errors caused by the depth of field effects coming from the limited thickness and the energy distribution of the laser sheet. The mean intensity of the individual droplets and the line profile of the LIF signal around the droplet edge were inspected for screening the laser sheet-straddling large-sized droplets. In order to consider the effects of the size-dependent LIF signal intensity, the size-classified or ensemble-averaged mean intensity of the individual droplets was introduced. The mean droplet sizes such as AMD and SMD were calculated using only screened droplets, and they increase a little before considering the depth of field effects.