Method to reduce errors of droplet sizing based on the ratio of fluorescent and scattered light intensities (laser-induced fluorescence/Mie technique)

摘要

The droplet sizing accuracy of the laser technique, based on the ratio of laser-induced fluorescence (LIF) and scattered light (Mie) intensities from droplets, is examined. We develop an analytical model of the ratio of fluorescent to scattered light intensities of droplets, which shows that the LIF/Mie technique is susceptible to sizing errors that depend on the mean droplet size and the spread of the droplet size distribution. The sizing uncertainty due to the oscillations of the scattered light intensity as a function of droplet size is first quantified. Then, a new data processing method is proposed that can improve the sizing uncertainty of the technique for the sprays that were examined in this study by more than 5percent by accounting for the size spread of the measured droplets, while improvements of 25percent are possible when accounting for the mean droplet size. The sizing accuracy of the technique is evaluated in terms of the refractive index of liquid, scattering angle, and dye concentration in the liquid. It is found that the proposed approach leads to sizing uncertainty of less than 14percent when combined with light collection at forward scattering angles close to 60 deg and the lowest fluorescent dye concentration in the liquid for all refractive indices.