Measurement of spray flow by an improved Interferometric Laser Imaging Droplet Sizing (ILIDS) system

Abstract

This paper describes a novel technique for droplet-sizing of spray. In the field of spray analysis, various kinds of measurement techniques have been proposed. Among them the method (ILIDS) provides instantaneous spatial distributions of droplet images in a frame of pictures as shown in the previous investigations (König et al. 1986, Glover et al. 1995, Skippon et al. (1996). The interferometric fringes in the projected image are correlated to its own droplet size, and the accuracy depends on the technique estimating the size of the circular image and the fringe spacing. The previous works have employed, in this sense, a high-resolution photography.

The present study proposes an automated system for high speed processing to improve the method employing a high resolution CCD camera and computing system so that the validation and accurate evaluation of fringe spacing may be easily performed by FFT.

The images to be taken were compressed optically to those of broken lines of length by defocused image and to thin width by focused image. The present novel ILIDS receiving optical system achieves the measurements of sizing in a denser spray by avoiding overlapping of neighboring images with fringe. The processing is performed scanning the image line in the frame and the fringe spacing from the periodic signal similar to the LDA burst signal. The system examined mono-disperse spray droplets and the resultant error with a comparison to a photographic measurement is estimated as less than 3% for arithmetic mean diameter distribution. The simultaneous measurement of droplet size and velocity is possible by using a two-dimensional PIV/PTV technique.