Abstract
Structured laser illumination planar imaging (SLIPI)-based techniques have been employed during the past decade for addressing multiple light scattering issues in spray imaging. In this article, SLIPI droplet sizing based on the intensity ratio of laser-induced fluorescence (LIF) over Mie scattering (SLIPI-LIF/Mie) and SLIPI-Scan for extinction-coefficient (µe) mapping are applied simultaneously. In addition, phase Doppler anemometry (PDA) and numerical calculations based on the Lorenz–Mie theory are also employed in order to extract the droplets Sauter mean diameter (SMD), the droplets number density (N), and the liquid volume fraction (LVF) in a steady asymmetric hollow cone water spray. The SLIPI-LIF/Mie ratio is converted to droplets SMD by means of a calibration procedure based on PDA measurements. The droplet SMD for the investigated spray varies from 20 µm to 60 µm, the N values range from 5 to 60 droplets per mm3, and the LVF varies between 0.05 × 10−4 and 5.5 × 10−4 within the probed region of the spray. To generate a series of two-dimensional images at different planes, the spray scanning procedure is operated in a “bread slicing” manner by moving the spray perpendicularly to the light sheet axis. From the resulting series of images, the procedure described here shows the possibility of obtaining three-dimensional reconstructions of each scalar quantity, allowing a more complete characterization of droplet clouds forming the spray region.
Highlights
Atomizing sprays are used for many industrial processes such as in internal combustion engines, crop treatment in agriculture, spray painting, production of powder in the food and pharmaceutical industry, etc. [1,2]
Spray quantities such as droplets SMD (Sauter mean diameter) give the information on the active surface area of the spray, while the liquid volume fraction (LVF) provides the spatial distribution of liquid in the spray
It is worth highlighting that the intensity contribution from the multiply scattered light is very difficult to predict and the observed differences between conventional and Structured laser illumination planar imaging (SLIPI) showed in [21] can change with the collection angle, optical turbidity, droplets size, distribution of the droplets in the spray, etc
Summary
Atomizing sprays are used for many industrial processes such as in internal combustion engines, crop treatment in agriculture, spray painting, production of powder in the food and pharmaceutical industry, etc. [1,2]. For the LVF mapping in sprays, Deshmukh and Ravikrishna [12] used planar laser-induced fluorescence combined with particle and droplet image analysis In this method, backlight illumination microscopic imaging-based calibration of LVF was implemented on macroscopic planar LIF and Mie images (recorded one after another; not simultaneously). It is worth highlighting that the intensity contribution from the multiply scattered light is very difficult to predict and the observed differences between conventional and SLIPI showed in [21] can change with the collection angle, optical turbidity, droplets size, distribution of the droplets in the spray, etc.
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