Mixing and evaporation analysis of a high-pressure SCR system using a hybrid LES-RANS approach

Kaario, Ossi; Vuorinen, Ville; Zhu, Lei; Larmi, Martti; Liu, Ronghou

doi:10.1016/j.energy.2016.11.138

Cited by 28 publications

(22 citation statements)

References 32 publications

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“…In particular for LES, a coupling between the Lagrangian particle tracking (LPT) and LES is usually utilized to model the atomized Lagrangian fuel droplets which lie in the subgrid range and to take their interactions with the surrounding carrier phase into account [18,19]. In addition, to avoid extreme computational costs, one common approach is to implicitly consider the primary breakup by introducing Lagrangian droplets with particular injection parameters and size distributions into a small cylindrical injection volume which is larger than actual fuel nozzle dimensions [20,21].…”

Section: Introductionmentioning

confidence: 99%

Large-Eddy Simulation of ECN Spray A: Sensitivity Study on Modeling Assumptions

et al. 2020

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In this study, various mixing and evaporation modeling assumptions typically considered for large-eddy simulation (LES) of the well-established Engine Combustion Network (ECN) Spray A are explored. A coupling between LES and Lagrangian particle tracking (LPT) is employed to simulate liquid n-dodecane spray injection into hot inert gaseous environment, wherein Lagrangian droplets are introduced from a small cylindrical injection volume while larger length scales within the nozzle diameter are resolved. This LES/LPT approach involves various modeling assumptions concerning the unresolved near-nozzle region, droplet breakup, and LES subgrid scales (SGS) in which their impact on common spray metrics is usually left unexplored despite frequent utilization. Here, multi-parametric analysis is performed on the effects of (i) cylindrical injection volume dimensions, (ii) secondary breakup model, particularly Kelvin–Helmholtz Rayleigh–Taylor (KHRT) against a no-breakup model approach, and (iii) LES SGS models, particularly Smagorinsky and one-equation models against implicit LES. The analysis indicates the following findings: (i) global spray characteristics are sensitive to radial dimension of the cylindrical injection volume, (ii) the no-breakup model approach performs equally well, in terms of spray penetration and mixture formation, compared with KHRT, and (iii) the no-breakup model is generally insensitive to the chosen SGS model for the utilized grid resolution.

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Section: Introductionmentioning

confidence: 99%

Large-Eddy Simulation of ECN Spray A: Sensitivity Study on Modeling Assumptions

et al. 2020

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“…Broadly speaking, a hybrid URANS/LES method should be based on the ability to adapt its behavior by applying the best-fitting modeling option with respect to the available numerical resolution. In the past 10 years, the number of engine-related hybrid modeling applications has been constantly increasing [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26], but hybrid/LP investigations are almost absent [27,28]. In our study, we evaluated two previously developed hybrid scale-resolving approaches [21,24,28,29] for a computational analysis of the "Spray G" reference GDI injector [30].…”

Section: Introductionmentioning

confidence: 99%

Evaluation of a Scale-Resolving Methodology for the Multidimensional Simulation of GDI Sprays

2019

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The introduction of new emissions tests in real driving conditions (Real Driving Emissions—RDE) as well as of improved harmonized laboratory tests (World Harmonised Light Vehicle Test Procedure—WLTP) is going to dramatically cut down NOx and particulate matter emissions for new car models that are intended to be fully Euro 6d compliant from 2020 onwards. Due to the technical challenges related to exhaust gases’ aftertreatment in small-size diesel engines, the current powertrain development trend for light passenger cars is shifted towards the application of different degrees of electrification to highly optimized gasoline direct injection (GDI) engines. As such, the importance of reliable multidimensional computational tools for GDI engine optimization is rapidly increasing. In the present paper, we assess a hybrid scale-resolving turbulence modeling technique for GDI fuel spray simulation, based on the Engine Combustion Network “Spray G” standard test case. Aspects such as the comparison with Reynolds-averaged methods and the sensitivity to the spray model parameters are discussed, and strengths and uncertainties of the analyzed hybrid approach are pointed out. The outcomes of this study serve as a basis for the evaluation of scale-resolving turbulence modeling options for the development of next-generation directly injected thermal engines.

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“…Although diverse operating conditions have been considered in the literature as reviewed in [7][8][9]19], it is noteworthy that the effect of turbulence modulation on the evaporation and thermal decomposition process has not yet been really investigated in SCR systems. In [20] only the effect of turbulence on the droplet trajectory by means of a dispersion model within the RANS framework has been reported.…”

Section: Introductionmentioning

confidence: 99%

“…However, the most of these works focused solely on retrieving the evaporation and thermal decomposition of UWS along with the ammonia conversion rate in mono-disperse UWS sprays using RANS models without particular consideration of turbulent flow modulation process. Only recently, hybrid LES/RANS (HLR) [19] and full LES [23] approaches have been implied to accurately describe the gas phase processes far around the droplet.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2019

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The selective catalytic reduction (SCR) methodology is notably recognized as the widely applied strategy for NOX 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 (NH3) gas generated by urea decomposition is intended to reduce NOX emission in the SCR system, it is apparent for the prediction of high NOX removal performance that UWS injector system which allows to realize such operating conditions is favorable to support high conversion efficiency of urea into NH3.

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Mixing and evaporation analysis of a high-pressure SCR system using a hybrid LES-RANS approach

Cited by 28 publications

References 32 publications

Large-Eddy Simulation of ECN Spray A: Sensitivity Study on Modeling Assumptions

Large-Eddy Simulation of ECN Spray A: Sensitivity Study on Modeling Assumptions

Evaluation of a Scale-Resolving Methodology for the Multidimensional Simulation of GDI Sprays

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

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