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.
Highlights
Laser diagnostics for spray characterization has been well established in the area of fuel injection and mixture formation in both CI (Compression Ignition) and SI (Spark Ignition) engines
NOx reduction efficiency strongly depends on the quality of mixing urea-water solution (UWS) with surrounding exhaust gases
The accurate measurement methods for fast and reliable UWS sprays characterization are of high importance in terms of spray pattern and injection process optimization
Summary
Laser diagnostics for spray characterization has been well established in the area of fuel injection and mixture formation in both CI (Compression Ignition) and SI (Spark Ignition) engines. We used several techniques which allowed both, global and local spray characterization: shadowgraphy-based long distance microscopy, high speed imaging of Mie scattering (scattering on the gas-liquid interface), LIF/Mie (Laser Induced Fluorescence together with Mie scattering). 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. This feature is important in terms of proper droplet size distribution determination especially when the range of droplet sizes is relatively wide. The results were compared with conventional Mie signals in order to conclude on the effects of multiple scattering on detected Mie signal and recognize the potential of this technique in LIF/Mie droplet sizing in the area of SCR sprays, what is planned to be done in near future
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