Interferometric laser imaging for droplet sizing: a method for droplet-size measurement in sparse spray systems

Abstract

A full-field, time-resolved interferometric method for the characterization of sparse, polydisperse spray systems is reported. The method makes use of the angular intensity oscillations in the wide-angle forward-scatter region. A pulsed laser is used to illuminate a planar sheet through the spray, which is imaged, out of focus, from the 45°direction. The image consists of a set of out-of-focus spots, each of which represents an individual droplet, and superimposed on which is a set of fringes corresponding to the angular intensity oscillations of that droplet. Macrophotographic recording with high-resolution digitization for image analysis provides a full-field capability. The spatial frequency of fringes on each spot in the image plane is dependent on the diameter of the corresponding droplet in the object plane, and a simple geometric analysis is shown to be appropriate for the calculation of the spatial frequency of fringes as a function of droplet size. Images are analyzed automatically by a software suite that uses Gaussian blur, Canny edge detection, and Hough transforms to locate individual droplets in the image field. Fringe spatial frequency is then determined by least-squares fitting to a Chirp function. The method is applicable to droplets with diameters in the range of several millimeters to several hundred millimeters and number densities of up to 10(3) to 10(4). The accuracy of the method for droplet-size determination has been evaluated by measurements of monodisperse aerosols of known droplet size, and measurements of droplet-size distribution in a polydisperse aerosol produced by a gasoline fuel injector are also presented. An extension of the method, using high-speed photography to measure two components of velocity in addition to size and position, is discussed. A two-wavelength approach may also offer the capability to measure the concentration of model fuel additives in droplets, and the results of a feasibility study are described.

Designing a maximum precision interferometric particle imaging set-up

“…When the out-focus image is a disk, a Hough transform can be used as was done by Glover et al (1995). This leads to the following formula:…”

An improved size and refractive index measurement of a pentadecane single droplet in a heated chamber

“…The fuel droplet behaviors including size and refractive index are important parameters for the evaluation of the characteristics and behaviors of fuel droplets in a combustion chamber. Various droplet behaviors have been investigated such as evaporation by Wilms [1], size by Glover et al [2], temperature by Castanet et al [3,4] and refractive index and rainbow angle (for refractive index determination) by Roth et al [5,6] and Anders et al [7]. In addition, droplet temperatures and droplet fractions of the components inside the droplet as in the case of multi-component droplets can be determined from the measured refractive index value.…”

“…In addition, droplet temperatures and droplet fractions of the components inside the droplet as in the case of multi-component droplets can be determined from the measured refractive index value. Numerous techniques have been adapted to examine the single droplet characteristics and behaviors including MSI (Mie Scattering Imaging) by Wilms [1], Laser Imaging for Droplet Sizing (ILIDS) by Glover et al [2], Kobayashi et al [8] and Kawaguchi et al [9], Phase Doppler Anemometry (PDA) by Fieberg et al [10], Sangkaew [11] and Fandrey et al [12]. Not only the experimental method can be used to investigate the droplet behaviors, but also the numerical calculations [13] or both the experimental and numerical calculations as well [8].…”

“…Glover et al [2] have performed on the large droplet size in several millimeters to several hundred millimeters using the angular intensity oscillations in the wide-angle forward-scatter region method, which are not suitable for the interpretation of the real fuel droplet condition in the combustion chamber in which the droplet size is in the micron scale (10-240 µm) [14]. This gave the insufficient information for an accurate evaluation of the fuel droplet size in the real system.…”

Extended glare point velocimetry and sizing for bubbly flows

“…Another, more recent technique in droplet diagnostics is Interferometric Laser Imaging for Droplet Sizing (ILIDS) (Koenig et al (1986); Glover et al (1995)), which is also known under various different names as IPI (Interferometric Particle Imaging) in Damaschke et al (2002a) or PPIA (Planar Particle Image Analysis) in Hess (1998). It is based on the interference pattern observed when reflection and refraction spots on the droplet surface (glare points) are seen out-of-focus.…”