Identification of Film Breakup for a Liquid Urea-Water-Solution and Application to CFD

Quissek, Max; Lauer, Thomas; García-Afonso, Óscar; Fowles, Stewart

doi:10.4271/2019-01-0983

Cited by 17 publications

(10 citation statements)

References 8 publications

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“…The We-number was chosen for the current study based on various examples in the literature and experience from previous investigations [8]. As shown in Equation (1), this calculation is based on the wall-normal component of the velocity v n , droplet diameter d, density ρ, and surface tension σ. For specification of the temperature, the absolute surface temperature was used.…”

Section: Impingement Characterizationmentioning

confidence: 99%

“…This comprises the spray injection and primary breakup, droplet impingement, film formation and propagation, evaporation, and reaction of urea to gaseous ammonia via thermolysis and hydrolysis. Prior investigations by the authors underlined the importance of the impingement process in SCR simulation [1]. The interaction of the spray droplets with a hot wall significantly influences the ammonia preparation and mixing with the exhaust gas.…”

Section: Introduction 1motivationmentioning

confidence: 99%

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Impact of Surface Roughness on the Impingement of Urea–Water Solution Droplets

Quissek

Lauer

2023

Fluids

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The understanding of impingement processes is crucial for optimizing automotive selective catalytic reduction (SCR) systems. An accurate description of this behavior helps design exhaust systems and increases the validity of modeling approaches. A component test bench was set up, featuring a droplet chain generator for producing droplet sizes typically found in the urea–water solution sprays of SCR systems. A heatable impingement plate with an interchangeable surface enabled investigation of the influence of surface roughness. Data were acquired using a high-speed camera and image postprocessing. The droplet–wall interaction could be described using different regimes. An approach to characterizing impingement behavior based on weighted-regime superposition enabled gradual transitions between regimes, instead of step-like changes. It was observed that the surface roughness increased the droplet–solid contact area and generated thermal-induced secondary droplets at lower temperatures. A region of enhanced mechanical disintegration of the droplet was found, caused by peaks of the surface shearing off parts of the droplet. The probability of a droplet rebounding from the wall was reduced on a rough surface, due to the interference of the surface spikes with the droplet’s spreading and contracting motion. Additionally, the influence of surface topography was investigated using a shot-peened surface. Caused by this surface’s reduced root mean square slope, the aforementioned enhancement of mechanical disintegration was not observed.

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Section: Impingement Characterizationmentioning

confidence: 99%

Section: Introduction 1motivationmentioning

confidence: 99%

Impact of Surface Roughness on the Impingement of Urea–Water Solution Droplets

Quissek

Lauer

2023

Fluids

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“…Good simulation results were achieved in the past, using the established impingement models, e.g., those of Bai and Gosman, or Birkhold [2,3,16] and model extensions [17,18]. However, validation against experimental data revealed shortcomings in certain areas or under specific conditions.…”

Section: Impingement Modelingmentioning

confidence: 99%

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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“…These values cover the temperature range with the highest changing gradients of the sticking mass. Below the surface temperature of 160°C, the temperature impact on droplet impingement is considered as negligible [44].…”

Section: Calculation Of the Source Terms Of The Fluid Film Phasementioning

confidence: 99%

Deposit Formation from Urea Injection: a Comprehensive Modeling Approach

Budziankou

Börnhorst

Kuntz

et al. 2020

Emiss. Control Sci. Technol.

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Long-term reliability is one of the major requirements for automotive exhaust aftertreatment systems with selective catalytic reduction (SCR) using urea water solution (UWS) as NH 3 carrier fluid. A high injection rate of UWS or unfavorable operating conditions may lead to formation of solid deposits, which decrease system efficiency by increasing backpressure and impairing ammonia uniformity. A reliable numerical prediction of deposit formation in urea SCR systems is desired for optimization of system design. However, comprehensive modeling of physical and chemical processes in the tailpipe as well as different time scale phenomena represents a challenging task. This study presents a comprehensive approach for modeling UWS injection, droplet impingement, liquid film and deposit formation based on CFD-simulation. An existing kinetic model for urea decomposition is integrated into the CFD code to predict solid by-product formation from wall films. Physical simulation time is extensively increased by substituting the Lagrange-particles with source terms of mass, momentum and energy reducing simulation time by a factor of 20. The comparison of measured and simulated results shows the capability of the presented modeling approach to predict position and chemical composition of solid deposits.

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Identification of Film Breakup for a Liquid Urea-Water-Solution and Application to CFD

Cited by 17 publications

References 8 publications

Impact of Surface Roughness on the Impingement of Urea–Water Solution Droplets

Impact of Surface Roughness on the Impingement of Urea–Water Solution Droplets

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

Deposit Formation from Urea Injection: a Comprehensive Modeling Approach

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