Reliable LIF/Mie droplet sizing in sprays using structured laser illumination planar imaging

Mishra, Yogeshwar Nath; Kristensson, Elias; Berrocal, Edouard

doi:10.1364/oe.22.004480

Cited by 63 publications

(66 citation statements)

References 26 publications

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“…From this data set, a final demodulated SLIPI image can be extracted, wherein the contribution from the multiply scattered light has been reduced (Berrocal et al 2008). However, due to the need for recording three sub-images, SLIPI has been mostly used for temporally averaged measurements of spray quantities such as droplet SMD in sprays (Mishra et al 2014), 3D-mapping of the droplet extinction coefficient (Wellander et al 2011), spray temperature using two-color LIF , as well as flame temperature using Rayleigh thermometry (Kempema and Long 2014). Note that SLIPI has also been demonstrated for 'instantaneous' imaging of rapidly occurring events (Kristensson et al 2010).…”

Section: Introductionmentioning

confidence: 99%

Comparison between two-phase and one-phase SLIPI for instantaneous imaging of transient sprays

et al. 2017

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images with an intensity profile close to the corresponding single scattering case. Experimentally, this suppression renders both an improvement in image contrast and the removal of undesired stray light components that could be interpreted as signal. However, while 2p-SLIPI preserves most of the initial spatial resolution, 1p-SLIPI results in a loss of spatial resolution, where high-frequency image information is not visible anymore. Thus, there is a tradeoff between preserving the most detailed information of the spray structure-with 2p-SLIPI-and being able to record an SLIPI image from a single modulated image only-with 1p-SLIPI. The comparison and technical overview of these two methods presented in this paper can facilitate in selecting which approach is the most suitable for a given application for spray visualization.

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Section: Introductionmentioning

confidence: 99%

Comparison between two-phase and one-phase SLIPI for instantaneous imaging of transient sprays

et al. 2017

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“…The multiple scattering effects are especially strong in case of optically dense sprays like non-evaporating diesel spray, where more than 65 % of multiple light scattering is usually detected [12]. However, even in fairly dilute spray, where single scattering events are in majority, the conventional LIF/Mie technique still remains largely affected by errors introduced by multiple light scattering [13]. Structured Laser Illumination Planar Imaging (SLIPI) technique is an illumination and processing method which can remove signal coming from scattering at the droplets located outside illuminated area and therefore limits the errors caused by multiple scattering.…”

Section: Introductionmentioning

confidence: 99%

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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“…Recent findings of Berrocal [4] and Mishra [5] show that even in fairly dilute sprays effects of multiple scattering. Therefore, additionally Mie signals were captured using structured illumination.…”

Section: Introductionmentioning

confidence: 99%

Laser diagnostics for urea-water solution spray characterization

Kapusta

Teodorczyk

2017

MATEC Web Conf.

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Abstract. In this study, we summarize the laser techniques used for urea-water solution (UWS) spray characterization at the Institute of Heat Engineering (ITC), Faculty of Power and Aeronautical Engineering at Warsaw University of Technology. In presented studies several techniques for both, global and local spray characterization were used. Shadowgraphy-based long distance microscopy was used to visualize individual droplets and primary breakup. High speed imaging of Mie scattering (scattering on the gas-liquid interface) signal was used for global spray characterization. Combination of LIF (Laser Induced Fluorescence) and Mie scattering allowed to determine qualitative droplet size distribution across the whole spray cloud. The structured illumination technique used to modulate laser light sheet allowed to minimize the effects of multiple scattering in detection of Mie signal, what indicated huge potential of this technique in characterization of UWS sprays. The results presented here prove the importance of laser diagnostics in SCR systems development.

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Reliable LIF/Mie droplet sizing in sprays using structured laser illumination planar imaging

Cited by 63 publications

References 26 publications

Comparison between two-phase and one-phase SLIPI for instantaneous imaging of transient sprays

Comparison between two-phase and one-phase SLIPI for instantaneous imaging of transient sprays

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

Laser diagnostics for urea-water solution spray characterization

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