Numerical evaluation of droplet sizing based on the ratio of fluorescent and scattered light intensities (LIF/Mie technique)

Charalampous, Georgios; Hardalupas, Y.

doi:10.1364/ao.50.001197

Cited by 30 publications

(39 citation statements)

References 42 publications

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“…The advantage of this method in reduced measuring times comes along with various challenging issues, such as accuracy limited by multiple-scattering, absorption effects and calibration procedures [10]. The calibration procedure is especially difficult for 90 deg detection angle since increase of the scattered light intensity with the droplet diameter is irregular [11]. Therefore, LIF/Mie ratio results shown in this study shall treated as qualitative indicator, not as direct SMD result.…”

Section: Introductionmentioning

confidence: 96%

LIF/Mie Droplet Sizing of Water Sprays from SCR System Injector using Structured Illumination

Kapusta

2017

Proceedings ILASS–Europe 2017. 28th Conference on Liquid Atomization and Spray Systems

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Recent trends in SCR (Selective Catalytic Reduction) systems development increase requirements for UWS (Urea Water Solution) injection. Close-coupled SCR system designs decrease the distance available for water evaporation and urea decomposition. Due to that, much effort is put into static mixing elements design improvement and injection process enhancement. So far, most experimental studies on UWS spray formation were based on Mie scattering visualization using global illumination and shadowgraphy imaging. High speed imaging of Mie signal with global illumination allows to determine global spray parameters such as penetration and angle but does not give information on droplet sizes. Droplet size determination, due to relatively large droplets generated by SCR injectors, can be done with Mie scattering or backlight imaging methods. Then the visualized area becomes narrowed since high magnification is required. Determination of droplet size distribution across whole spray in such arrangement requires number of measurements. LIF/Mie (Laser Induced Fluorescence/Mie scattering) technique provides an attractive alternative for rapid determination of droplet size distribution across the whole spray. This method however suffers from multiple scattering effects which might affect droplet size distribution results even in relatively dilute sprays. In this study, LIF/Mie ratio distribution across sprays from commercial automotive injector for SCR systems was determined by simultaneous LIF and Mie detection using structured illumination. Moreover, the results were compared with conventional LIF/Mie imaging. Nd:YAG pulse laser was used as a light source. Second harmonic beam of 532 nm was used to illuminate the sprays. Instead of UWS pure water doped with Eosin Y was used. The results showed that conventional images exhibited much stronger background signal. Moreover, the conventional imaging was sensitive to reflections from experimental setup elements, specifically reflections from LIF camera filter. These two observations prove the importance of using SLIPI for LIF/Mie droplets sizing in sprays for SCR systems. At the same time the obtained results showed that under certain conditions (no accidental reflections in the background) conventional imaging provides similar LIF/Mie ratio as structured illumination. The results showed that the LIF/Mie ratio remains unchanged over the spray cloud. This suggests that SMD remains unchanged as well. The slight increase of LIF/Mie ratio far from the injector outlet could be caused by absence of small droplets due to lower momentum and thus lower penetration distance. This assumption however should be verified with PIV measurement.

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Section: Introductionmentioning

confidence: 96%

LIF/Mie Droplet Sizing of Water Sprays from SCR System Injector using Structured Illumination

Kapusta

2017

Proceedings ILASS–Europe 2017. 28th Conference on Liquid Atomization and Spray Systems

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“…Attenuation of the scattered light intensity as it propagates from the illuminated droplets to the detector 3. Multiple scattering of the scattered light initiated from one droplet on other droplets in the spray These have been considered by many researchers and various approaches have been proposed to address them as the measurement accuracy of the LIF/Mie technique (Yeh, Kosaka et al 1993;Sankar, Maher et al 1999) is sensitive to the scattered light intensity (Charalampous and Hardalupas 2011a;Charalampous and Hardalupas 2011b;Charalampous and Hardalupas 2012).…”

Section: Data Processing Methodologymentioning

confidence: 99%

“…A planar droplet sizing technique (also know as optical patternator) has been proposed for the measurement of the Sauter mean diameter (SMD) of spray droplets, based on combined laser-induced fluorescence and scattered light (LIF/Mie) intensity imaging on a plane of a spray determined by a laser sheet (Yeh, Kosaka et al 1993;Kamimoto 1994;Le Gal, Farrugia et al 1999;Sankar, Maher et al 1999;Domann and Hardalupas 2003;Zimmer, Domann et al 2003;Charalampous and Hardalupas 2011a;Charalampous and Hardalupas 2011b). The LIF/Mie technique has a significant advantage over other droplet sizing methods in that it is a planar technique that can size full planes of sprays, while the other methods are limited to "point" (Phase Doppler Velocimetry, PDV), line of sight (laser diffraction), or planes of small cross-sectional areas (Interferometric Laser Imaging Droplet Sizing, ILIDS) of sprays.…”

Section: Introductionmentioning

confidence: 99%

Planar Droplet Sizing in Dense Sprays

Hardalupas¹

2013

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Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing the burden, to Department of Defense, Washington Headquarters Services, Directorate for Information , 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. REPORT DATE (DD-MM-YYYY)8 April 2013 (From -To) REPORT TYPE Final Report DATES COVERED PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)Imperial College of Science Technology and Medicine Exhibition Road London, U K SW7 2BT PERFORMING ORGANIZATION REPORT NUMBERN/A SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)EOARD Unit 4515 BOX 14 APO AE 09421 SPONSOR/MONITOR'S ACRONYM(S)AFRL/AFOSR/IOE (EOARD) SPONSOR/MONITOR'S REPORT NUMBER(S) AFRL-AFOSR-UK-TR-2013-001512. DISTRIBUTION/AVAILABILITY STATEMENT Distribution A: Approved for public release; distribution is unlimited. SUPPLEMENTARY NOTES ABSTRACTAn investigation was undertaken to examine the application of a laser beam scanning methodology on the measurement of the time-averaged spray spatial structure. This approach can directly reduce secondary light scattering effects from the spray droplets and can take into account probe laser beam and scattered light intensity attenuation in order to reduce associated uncertainties on the spray characteristics. Evaluation of two approaches was performed, where one considered scanning the probe laser beam across the spray and the other considered traversing the spray while the probing beam and the imaging optics were fixed. It is determined that for the purposes of evaluating the methodology for correcting quantitative measurement errors due to attenuation, the second approach is more appropriate. This is because scanning the beam would require constant refocusing of the imaging system to the probed region. Another issue is the changing imaging resolution as the distance between the probe laser beam and the imaging optics is constantly changing. By traversing the spray across the probe beam, both of the aforementioned effects are eliminated and the signal correction methodology can be applied directly. The scattered light intensity correction methodology was successfully applied to a flat spray with measurements close to the nozzle and beam probing along the long dimension of the spray, so that attenuation effects are more profound. It is determined that attenuation of the laser beam along the spray can be as high as 20% and attenuation of the measured int...

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“…This work showed that the scattering angle (Figure 1.c), the droplet size and the refractive index modify the proportionality between the scattering intensity and the droplet surface. In parallel, the influence of the concentration of fluorescent dye on the proportionality between the fluorescence intensity and the droplet volume [4] was demonstrated. Optimum values of the scattering angle and the fluorescent dye concentration were obtained to improve the sizing measurement accuracy [5,6] and recent studies compared the PDS measurements with the PDA ones [3,7].…”

Section: Planar Droplet Sizing (Pds)mentioning

confidence: 99%

“…A concentration of Rhodamine 6G of 1 mg/L was sufficient to give an exploitable fluorescent signal on the intensified camera. [4].…”

Section: Pds Implementation On An Aeronautical Swirled Spraymentioning

confidence: 99%

Planar droplet sizing: Application to a spray of Jet A1 kerosene

Doublet¹,

Lempereur²,

Bodoc³

et al. 2017

Proceedings ILASS–Europe 2017. 28th Conference on Liquid Atomization and Spray Systems

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Optical techniques are widely employed for their non-intrusive behavior and are applied to two-phase flow investigations. Until now, the most commonly used technique to determine the droplet size is the Phase Doppler Anemogranulometry, although it is time consuming for an overall injector characterization. An imaging technique called Planar Droplet Sizing has been used to offer an alternative and provide a spatially-resolved 2D map of the Sauter Mean Diameter (SMD). The measurement is based on the ratio between laser-induced fluorescence and scattered light intensities which are assumed to be proportional respectively to the droplet volume and droplet surface area. However, previous studies revealed that the dependence of fluorescence intensity on the droplet volume can be altered by the absorption of light in the liquid. The scattered light intensity depends on the scattering angle and intensity variations within the field of view must be avoided. The aim of this study is to make the PDS technique operational for a Jet A-1 kerosene spray. A strong absorption of liquid kerosene appears under UV excitation at 266 nm making the technique unsuitable. Under visible excitation at 532 nm, a fluorescent tracer (Pyrromethene 597) must be added to the kerosene to enhance the fluorescence signal. To prevent scattered light intensity variations within the field of view, an optimal scattering angle close to 115° is required. An image processing algorithm is proposed in order to reduce the effects of multiple scattering.

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Numerical evaluation of droplet sizing based on the ratio of fluorescent and scattered light intensities (LIF/Mie technique)

Abstract: The dependence of fluorescent and scattered light intensities from spherical droplets on droplet diameter was evaluated using Mie theory. The emphasis is

Cited by 30 publications

References 42 publications

LIF/Mie Droplet Sizing of Water Sprays from SCR System Injector using Structured Illumination

LIF/Mie Droplet Sizing of Water Sprays from SCR System Injector using Structured Illumination

Planar Droplet Sizing in Dense Sprays

Planar droplet sizing: Application to a spray of Jet A1 kerosene

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