Thermal Decomposition of a Single AdBlue ® Droplet Including Wall–Film Formation in Turbulent Cross-Flow in an SCR System

Kaushal Nishad, Marcus Stein, Florian Ries, Viatcheslav Bykov, Ulrich Maas, Olaf Deutschmann, Johannes Janicka and Amsini Sadiki
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Kaushal Nishad: Institute of Energy and Power Plant Technology, Technische Universität Darmstadt, 64287 Darmstadt, Germany
Marcus Stein: Institut für Technische Thermodynamik, Karlsruher Institut für Technologie, 76131 Karlsruhe, Germany
Florian Ries: Institute of Energy and Power Plant Technology, Technische Universität Darmstadt, 64287 Darmstadt, Germany
Viatcheslav Bykov: Institut für Technische Thermodynamik, Karlsruher Institut für Technologie, 76131 Karlsruhe, Germany
Ulrich Maas: Institut für Technische Thermodynamik, Karlsruher Institut für Technologie, 76131 Karlsruhe, Germany
Olaf Deutschmann: Institut für Technische Chemie und Polymerchemie, Karlsruher Institut für Technologie, 76131 Karlsruhe, Germany
Johannes Janicka: Institute of Energy and Power Plant Technology, Technische Universität Darmstadt, 64287 Darmstadt, Germany
Amsini Sadiki: Institute of Energy and Power Plant Technology, Technische Universität Darmstadt, 64287 Darmstadt, Germany

Energies, 2019, vol. 12, issue 13, 1-25

Abstract: The selective catalytic reduction (SCR) methodology is notably recognized as the widely applied strategy for NO X control in exhaust after-treatment technologies. In real SCR systems, complex unsteady turbulent multi-phase flow phenomena including poly-dispersed AdBlue ® spray evolve with a wide ranging relative velocity between the droplet phase and carrier gas phase. This results from an AdBlue ® spray that is injected into a mixing pipe which is cross-flowing by a hot exhaust gas. To reduce the complexity while gaining early information on the injected droplet size and velocity needed for a minimum deposition and optimal conversion, a single droplet with a specified diameter is addressed to mimic a spray featuring the same Sauter Mean Diameter. For that purpose, effects of turbulent hot cross-flow on thermal decomposition processes of a single AdBlue ® droplet are numerically investigated. Thereby, a single AdBlue ® droplet is injected into a hot cross-flowing stream within a mixing pipe in which it may experience phase change processes including interaction with the pipe wall along with liquid wall–film and possible solid deposit formation. First of all, the prediction capability of the multi-component evaporation model and thermal decomposition is evaluated against the detailed simulation results for standing droplet case for which experimental data is not available. Next, exploiting Large Eddy Simulation features the effect of hot turbulent co- and cross-flowing streams on the dynamic droplet characteristics and on the droplet/wall interaction is analyzed for various droplet diameters and operating conditions. This impact is highlighted in terms of droplet evaporation time, decomposition efficiency, droplet trajectories and wall–film formation. It turns out that smaller AdBlue ® droplet diameter, higher gas temperature and relative velocity lead to shorter droplet life time as the droplet evaporates faster. Under such conditions, possible droplet/wall interaction processes on the pipe wall or at the entrance front of the monolith may be avoided. Since the ammonia (NH 3 ) gas generated by urea decomposition is intended to reduce NO X emission in the SCR system, it is apparent for the prediction of high NO X removal performance that UWS injector system which allows to realize such operating conditions is favorable to support high conversion efficiency of urea into NH 3 .

Keywords: AdBlue ® injection; large eddy simulation; Eulerian–Lagrangian approach; thermal decomposition; wall–film formation; conversion efficiency (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2019
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