Experimental investigation on the injection of an urea–water solution in hot air stream for the SCR application: Evaporation and spray/wall interaction

Grout, Sébastien; Blaisot, Jean‐Bernard; Pajot, K.; Osbat, Giovanni

doi:10.1016/j.fuel.2012.09.022

Cited by 85 publications

(41 citation statements)

References 13 publications

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“…As shown by Grout et al [1], even direct Mie scattering imaging can be used to determine the size of individual droplets. They used this approach to determine temporal change of the droplet size and calculate the evaporation rate according to Dsquare evaporation law.…”

Section: Introductionmentioning

confidence: 99%

“…They used this approach to determine temporal change of the droplet size and calculate the evaporation rate according to Dsquare evaporation law. Commonly used method for individual droplets visualization is backlight imaging (shadowgraphy) [1,2]. This method coupled with long distance microscopy allows to visualize individual droplets of diameter lower than 10 µm provided that the spray is not optically dense.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Laser diagnostics for urea-water solution spray characterization

Kapusta

Teodorczyk

2017

MATEC Web Conf.

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“…Thus, broad variety of measurement techniques can be used for droplet size determination starting from Mie scattering [8], backlight imaging [8,9], ending up with PDA (Phase Doppler Anemometry) [9] and LIF/Mie. Grout et al [8] used Mie scattering to determine the size of individual droplets and calculate the evaporation rate according to D-square evaporation law. The droplets taken into account for diameter calculation covered at least several pixels what made possible to directly determine their diameters basing on Mie scattering images.…”

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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“…Literature data essentially deal with the thermal decomposition [25,26] or hydrolysis mechanism of urea [9,13,27] (with or without catalysts). At a higher scale, some studies also focused on the simulation of the urea spray injection [28,29], using honeycomb supported catalysts and/or an industrial exhaust pipe. It was advanced that the residence time between urea injection zone and the catalytic bed can be a key parameter.…”

Section: Introductionmentioning

confidence: 99%

Use of a µ-Scale Synthetic Gas Bench for Direct Comparison of Urea-SCR and NH3-SCR Reactions over an Oxide Based Powdered Catalyst

et al. 2015

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Abstract:The selective catalytic reduction (SCR) of NOx by NH3 has been extensively studied in the literature, mainly because of its high potential to remediate the pollution of diesel exhaust gases. The implementation of the NH3-SCR process into passenger cars requires the use of an ammonia precursor, provided by a urea aqueous solution in the conventional process. Although the thermal decomposition and hydrolysis mechanisms of urea are well documented in the literature, the influence of the direct use of urea on the NOx reduction over SCR catalysts may be problematic. With the aim to evaluate prototype powdered catalysts, a specific synthetic gas bench adjusted to powdered material was developed, allowing the use of NH3 or urea as reductant for direct comparison. The design of the experimental setup allows vaporization of liquid urea at 200 °C under 10 bar using an HPLC pump and a micro injector of 50 μm diameter. This work presents the experimental setup of the catalytic test and some remarkable catalytic results towards further development of new catalytic formulations specifically dedicated to urea-SCR. Indeed, a possible divergence in terms of DeNOx efficiency is evidenced depending on the nature of the reductant, NH3 or urea solution. Particularly, the evaluated catalyst may not allow an optimal NOx conversion because of a lack in ammonia availability when the urea residence time is shortened. This is attributed to insufficient activity of isocyanic acid (HNCO) hydrolysis, OPEN ACCESSCatalysts 2015, 5 1536 which can be improved by addition upstream of an active solid for the hydrolysis reaction such as ZrO2. Thus, this µ-scale synthetic gas bench adjusted to powdered materials enables the specific behaviour of urea use for NOx reduction to be demonstrated.

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Experimental investigation on the injection of an urea–water solution in hot air stream for the SCR application: Evaporation and spray/wall interaction

Cited by 85 publications

References 13 publications

Laser diagnostics for urea-water solution spray characterization

Laser diagnostics for urea-water solution spray characterization

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

Use of a µ-Scale Synthetic Gas Bench for Direct Comparison of Urea-SCR and NH3-SCR Reactions over an Oxide Based Powdered Catalyst

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