A Fast Modeling Approach for the Numerical Prediction of Urea Deposit Formation

Budziankou, Uladzimir; Quissek, Max; Lauer, Thomas

doi:10.4271/2020-01-0358

Cited by 7 publications

(7 citation statements)

References 32 publications

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“…The box has a quadratic cross section of 200 × 200 mm and a length of 600 mm. At the inlet and the outlet of the box, an uncoated monolith is fitted to straighten the airflow through the box and achieve fine-scale isotropic turbulence, as shown in [42] A model of the box is visible in Figure 11 on the right-hand side. The exhaust gas enters the box from the left and streams along a stainless-steel plate positioned inside the box.…”

Section: Validation Case Surface Cooling 241 Experimental Setupmentioning

confidence: 99%

“…The boundary layer was resolved with seven prism layers to enable a low-y + -approach and capture the heat transfer correctly. A mesh sensitivity analysis was performed earlier as reported in [42] to select the approriate mesh. More details on the mesh, including figures, can be found in [42].…”

Section: Simulation Setupmentioning

confidence: 99%

“…A mesh sensitivity analysis was performed earlier as reported in [42] to select the approriate mesh. More details on the mesh, including figures, can be found in [42].…”

Section: Simulation Setupmentioning

confidence: 99%

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CFD Simulation of SCR Systems Using a Mass-Fraction-Based Impingement Model

Quissek

Budziankou

Pollak

et al. 2023

Fluids

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Computational fluid dynamics (CFD) are an essential tool for the development of diesel engine aftertreatment systems using selective catalytic reduction (SCR) to reduce nitrous oxides (NOx). In urea-based SCR, liquid urea–water solution (UWS) is injected into the hot exhaust gas, where it transforms into gaseous ammonia. This ammonia serves as a reducing agent for NOx. CFD simulations are used to predict the ammonia distribution in the exhaust gas at the catalyst inlet. The goal is to achieve the highest possible uniformity to realize homogeneous NOx reduction across the catalyst cross section. The current work focuses on the interaction of UWS droplets with the hot walls of the exhaust system. This is a crucial part of the preparation of gaseous ammonia from the injected liquid UWS. Following experimental investigations, a new impingement model is described based on the superposition of four basic impingement behaviors, each featuring individual secondary droplet characteristics. The droplet–wall heat transfer, depending on surface temperature and impingement behavior, is also calculated using a newly parameterized model. Applying the presented approach, the cooling of a steel plate from intermittent spray impingement is simulated and compared to measurements. The second validation case is the distribution of ammonia at the catalyst inlet of an automotive SCR system. Both applications show good agreement and demonstrate the quality of the new model.

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Section: Validation Case Surface Cooling 241 Experimental Setupmentioning

confidence: 99%

Section: Simulation Setupmentioning

confidence: 99%

See 1 more Smart Citation

CFD Simulation of SCR Systems Using a Mass-Fraction-Based Impingement Model

Quissek

Budziankou

Pollak

et al. 2023

Fluids

Self Cite

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show abstract

“…It should be stated that the described modeling strategy is a compromise between accuracy and computational effort to evaluate the flow and spray dynamics, which is the focus of the numerical investigation in this work. More advanced modeling approaches would be needed to describe the detailed mechanism of deposit formation on the surfaces as demonstrated in the literature [27,28].…”

Section: Numerical Setupmentioning

confidence: 99%

Urea Conversion for Low‐Temperature Selective Catalytic Reduction in a Swirled Diesel Exhaust Gas Configuration

et al. 2022

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A novel design of an AdBlue mixing unit to reduce urea deposits at low temperatures in diesel exhaust is described. The main principle of the mixer includes the injection of AdBlue in an axisymmetric swirling flow, which is achieved by splitting the exhaust stream and off‐centred introduction of the sub‐flows. Crucial geometric parameters were analyzed by computational fluid dynamics (CFD) simulations towards pressure loss, flow field, and spray morphology. Deposit formation was experimentally investigated on three upscaling levels implying an optical test bench, a diesel engine test bench, and a hydraulic excavator. In particular, the studies with the hydraulic excavator showed neither deposits nor critical back pressure. Overall, the experiments substantiated the working principle of the AdBlue mixer.

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“…The second injection starts from a temperature slightly higher than the Leidenfrost temperature, then drops below this limit and shows a quick increase in the temperature gradient associated with the transition boiling regime. These temperature ranges can be dangerous in term of solid deposit formation, because of the high heat transfer coefficient involved in this phase change regime, that can quickly reduce the temperature of the components of the ATS and lead to the formation of a persisting liquid film, which is the main reason for solid deposit formation [31]. These large heat transfer coefficients can also be exploited to ensure quick evaporation of the film, if the heat subtracted by the evaporation can be quickly replenished between injections, with a hot gas EGR or a thermal resistor.…”

Section: Validation Test Casementioning

confidence: 99%

Modeling the Kinetic and Thermal Interaction of UWS Droplets Impinging on a Flat Plate at Different Exhaust Gas Conditions

Nappi¹,

Montenegro²,

Onorati³

et al. 2021

SAE Technical Paper Series

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T he selective catalytic reduction has seen widespread adoption as the best technology to reduce the NO x emissions from internal combustion engines, particularly for Diesels. This technology uses ammonia as a reducing agent, which is obtained injecting an ammonia carrier into the exhaust gas stream. The dosing of the ammonia carrier, usually AdBlue, is the major concern during the design and engine calibration phases, since the interaction between the injected liquid and the components of the exhaust system can lead to the undesired formation of solid deposits. To avoid this, the thermal and kinematic interaction between the spray and the components of the after treatment system (ATS) must be modeled accurately. In this work, the authors developed a Conjugate Heat Transfer (CHT) framework to model the kinetic and thermal interaction among the spray, the eventual liquid layer and the pipe walls. The Nukiyama curve has been embedded in the calculation of the heat flux between the droplet and the walls to limit the heat transfer in the proximity of the Leidenfrost point and in the transition region. To validate this model, an experimental data set was provided by EMPA (CH) and used for comparison with calculated values. The measurement of the thermal footprint of the spray have been performed on the back of a thin plate where the spray impinges. Several injections have been considered with the intent of showing the transition to the different interaction regimes. The simulations performed show that after the initial cooling of the wall, due to impingement, a liquid film is formed, which is then dragged along the plate. As the number of injection progresses, the effect of the transition between the different evaporation regimes translates into high temperature gradients on the back of the plate. The comparison with the experimental data both in terms of temperature and temperature gradient shows a good agreement with the experiments, showing the capabilities of the model developed to predict the temperature drop.

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A Fast Modeling Approach for the Numerical Prediction of Urea Deposit Formation

Cited by 7 publications

References 32 publications

CFD Simulation of SCR Systems Using a Mass-Fraction-Based Impingement Model

CFD Simulation of SCR Systems Using a Mass-Fraction-Based Impingement Model

Urea Conversion for Low‐Temperature Selective Catalytic Reduction in a Swirled Diesel Exhaust Gas Configuration

Modeling the Kinetic and Thermal Interaction of UWS Droplets Impinging on a Flat Plate at Different Exhaust Gas Conditions

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