Article

Integrated 1D to 3D Simulation Workflow of Exhaust Aftertreatment Devices

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Abstract

Future limits on emissions for both gasoline and Diesel engines require adequate and advanced systems for the after-treatment of the exhaust gas. Computer models as a complementary tool to experimental investigations are an indispensable part to design reliable after-treatment devices such as catalytic converters and Diesel particulate filters including their influence on the power-train. Therefore, the objective of this contribution is to present an integrated 1D to 3D simulation workflow of of catalytic converters and Diesel particulate filters. The novelty of this approach is that parameters or set of parameters, obtained by a fast and efficient 1D-gas exchange and cycle simulation code for power-trains (AVL (2002a)), are readily transferable onto a 3D general purpose simulation code (AVL (2002b)). Thus, detailed aspects such as spatial distribution of temperatures or heat losses are investigated with only a single effort to estimate parameters. This is based on identical models predicting flow, energy and conversion of species of the exhaust gas, employed to both the 1D gas exchange/cycle and the 3D CFD simulation code. This approach allows, in a first stage to carry out a basic analysis and to define first layouts for the exhaust system by the 1D gas exchange and cycle simulation code. Characteristic parameters of this stage are used for the multi-dimensional simulation to evaluate the overall performance including fine tuning of after-treatment systems. Thus, the life-time cycle of different layout concepts is reduced significantly.

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... The assumption of changes in channel geometry due to PM layer loading was revisited by Peters et al. (Peters 2003, Peters et al. 2004,b , Haralampous et al. 2004a, and recently by Depcik and Assanis (Depcik andAssanis 2008 , Depcik 2010 ). In particular, these works reflect a consideration of Bissett ' s original concept that the thickness of the PM layer does not influence the flow properties (1984 article, assumption # 5). ...
... It is not until the Peters et al. (Peters 2003, Peters et al. 2004 ) and Haralampous et al. articles (Haralampous et al. 2003,b,c,d,e , Haralampous and Koltsakis 2004a that the literature illustrates a merging of two models: channel and wall. These authors decide to include the wall species equations into the overall formulation instead of solving them separately. ...
... In the following 2 years, Peters et al. (Peters 2003, Peters et al. 2004 ) simulate the PM mass per unit length on the surface by including a flow of PM to the surface: ...
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... This was done using Dean and Nusselt correlations for vortices in centripetal flow domains. In addition to the 1D and 3D methodologies mentioned above, there has also been research on developing a 1D/3D hybrid model [29,30], but this was limited to a few sub-systems of the exhaust. Apart from the simulation of the complete exhaust system, there have been numerous studies on the thermal behavior of exhaust aftertreatment components, such as the catalytic converters [2,4,11,12,19,20,23,37]. ...
... With the objective of combining the advantages of both the approaches, a new hybrid methodology was developed. There have been a few studies in the past that explored this option [29,30]. However, those works have mainly focused on modelling parts of the exhaust system as a 1D/3D hybrid. ...
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... Under certain experimental conditions, all channels can be efficiently modeled in one dimension in the same way to meet the requirements (Kandylas et al. 2002;Peters et al. 2004). The reaction phenomena as well as heat and momentum transfer in the diesel particulate filter are described by a model that takes into account the thermophysical properties and geometry. ...
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... For an internal channel flow of DPF monolith, an axial gas velocity is so dominant compared to the radial velocity because of a large difference of aspect ratio of channel [20]. Hence the flow could be regarded as one dimensional channel flow. ...
... PM regeneration, respectively. The detailed explanation of the PM deposition process used in the present study is given in the literature[20]. The continuity equation and transport equations for the mass fractions of species in the PM layer are given in equations (29), (30), respectively. The source terms included in those equations are shown in equations (31), ...
Conference Paper
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... Coupling between zero-, one-, and three-dimensional simulations is very important for several tasks, e.g. engine modelling and exhaust aftertreatment [85], [86]. This allows adapting the level of modelling details to the current state of development. ...
... Coupling between zero-, one-, and three-dimensional simulations is very important for several tasks, e.g. engine modelling and exhaust aftertreatment [85], [86]. This allows adapting the level of modelling details to the current state of development. ...
... Most of the new developments in the filter channel scale phenomena simulation pertain to the mechanistic modelling of ash transport and deposition dynamics originally introduced in Konstandopoulos et al. (2003a). The same formalism can be applied to account for shear-induced soot particle re-entrainment and further downstream deposition (Peters, 2003). Experimental studies of ash deposition and transport in filters require extensive and costly engine runs and are scarce in the literature. ...
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... For an internal channel flow of DPF monolith, a gas velocity in axial direction is so dominant compared to a radial direction velocity that the flow could be regarded as one dimensional channel flow because of a big difference of aspect ratio of channel [8]. z component of momentum in the single channel model used in the present study is neglected in the porous wall because the transport of momentum perpendicular to the x direction in the porous wall is only a small fraction of the wall flow. ...
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Chapter
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Chapter
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Chapter
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Researchers have been using one-dimensional based models of diesel particulate filters (DPFs) for over two decades with good success in comparison to measured experimental data. Recent efforts in literature have expanded the classical model to account for the effects of varying soot layer thickness on the flow area of the gases. However, some discrepancies exist with respect to this formulation and the physical phenomena modeled in the channel equations. In addition, there is still some discussion regarding the calculation of the gas temperature within the soot and wall layers. As a result, this paper presents a model to discuss these different phenomena to remove or validate previous assumptions. In specific, formulation of the flow equations in area-conserved format (or quasi-one-dimensional) allows the model to account for the changes in the gaseous area as a function of soot loading. In addition, imposing thermodynamic equilibrium at the interface of the channels and wall layers allows the model to capture the thermal entrance lengths. These tasks were undertaken to illustrate whether or not the results justify the effort is worthwhile and this additional complexity needs to be incorporated within the model. By utilizing linear density interpolation in the wall to increase the computational efficiency of the code, it was determined that the classical model assumptions of neglecting soot thickness and gas temperature in the wall are valid within the range of typical DPF applications.
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This paper enhances an earlier publication by including the concentration equations of motion into the area-conserved one-dimensional based diesel particulate filter model. A brief historical review of the species equations is accomplished to describe this model and the pertinent physics involved. In the species equations through the wall and soot layers, the diffusion constants are modified to account for the close proximity of the porous walls and the particulate matter to the gas flowing through the accompanying layers. In addition, a review of potential options involving the diffusion velocity is accomplished to determine the effect of pressure gradients on this phenomenon. In the previous paper, the model formulation illustrated that a common assumption to make for an enthalpy difference is the use of constant pressure specific heat times a temperature difference. Because of the different heats of formation and sensible enthalpies associated with the chemical species, this assumption reviewed is found to have a related error. Finally, because each channel is treated as an open system, making the common assumption of dilute mixture simplification is reviewed and found to have an associated error.
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Résumé — La simulation 0D : une voie d'avenir pour traiter les problématiques de post-traitement des véhicules automobiles modernes — Dans les véhicules automobiles modernes, les systèmes de post-traitement deviennent incontournables pour respecter les nouvelles normes de pollution. De ce fait, les problématiques autour du post-traitement deviennent de plus en plus significatives sur le coût de développement des moteurs et des véhicules. À titre d'exemple, certains scenarii montrent que le système de post-traitement d'un véhicule Diesel Euro 6 pourrait être composé de 5 éléments différents. Cette architecture complexe implique le développement d'outils sophistiqués pour aider à la conception de la ligne de post-traitement et à la définition de stratégies de contrôle. Ce papier démontre que la simulation zéro-dimension (0D) peut être une approche pertinente pour développer des simulateurs d'organes de post-traitement compatibles avec les exigences de précision et de temps de calculs demandées. Un modèle de monolithe original zéro-dimension est également décrit. L'approche est basée sur des éléments résistifs et capacitifs comme définis dans la théorie bond-graph [Karnopp D.C., Margolis D.L., Rosenberg R.C. (1990) Systems dynamics: a unified approach, Second Edition, John Wiley & Sons, New-York]. Le modèle proposé prend en compte le comportement dynamique du fluide et le comportement thermique du monolithe. Plusieurs modèles de catalyseurs sont construits en associant ce modèle de monolithe avec des schémas réactionnels simplifiés tirés de la littérature [Koltsakis G.C., Konstandinis P.A., Stamatelos A.M. (1997) Development and application range of mathematical models for 3-way catalytic converters, Appl. Catal. B: Environ. 12, 161-191]. Diviser un modèle de monolithe en plusieurs blocs 0D élémentaires associés en série permet d'obtenir une bonne représentation de la dynamique présente à l'intérieur d'un catalyseur et d'accéder à des informations locales comme dans les modèles 1D avec des temps de calcul réduits [Depcik C., Assanis D. (2003) One-dimensional automotive catalyst modeling, Prog. Energ. Combust. 31, 308-369]. Cette approche peut être utilisée comme un moyen de compréhension de phénomènes complexes qui régissent le catalyseur impliquant plusieurs domaines de la physique. Elle représente aussi un outil de simulation pertinent dans la définition des architectures de ligne de post-traitement et dans le contrôle des émissions polluantes. Le potentiel de l'approche pour traiter l'ensemble des organes de post-traitement est illustré par des résultats sur un catalyseur trois voies (3WC), un catalyseur d'oxydation Diesel (DOC), un piège à NOx (LNT), un système de catalyse sélective des NOx (SCR) et un filtre à particules (DPF). Cette capacité à fournir avec un bon compromis temps/précision des informations intéressantes pour aider au développement de systèmes de post-traitement de plus en plus complexes rend la simulation 0D particulièrement attractive.
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A minimization of the maximum diesel particulate filter (DPF) wall temperature and fast light-off during regeneration are targets for a high durability of the DPF and a high efficiency of soot regeneration. A one-channel numerical model has been adopted in order to predict the transient thermal response of the DPF. The effect of the ratio of the length to diameter (L/D), cell density, the amount of soot loading on the temporal thermal response and regeneration characteristics have been numerically investigated under two representative running conditions: city driving mode and high speed mode. The results indicated that the maximum wall temperature of the DPF increased with increasing [`]L/D' in [`]high speed mode'. On the contrary, the maximum wall temperature decreases with increasing [`]L/D' in the range of [`]L/DÂ [greater-or-equal, slanted]Â 0.6' in [`]city driving mode'. The maximum temperature decreased with increasing cell density because heat conduction and heat capacity were increased. Before commencing soot regeneration, the maximum allowed soot loading for retaining DPF durability was about 140Â g (5.03Â kg/m3) under [`]city driving mode' and about 200Â g (7.19Â kg/m3) under [`]high speed mode' in this study. The effect of the amount of soot loading on light-off time was negligible.
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The use of a diesel particulate filter (DPF) in a diesel aftertreatment system has proven to be an effective and efficient method for removing particulate matter (PM) in order to meet more stringent emission regulations without hurting engine performance. One of the favorable PM regeneration technologies is the NO2-assisted regeneration method due to the capability of continuous regeneration of PM under a much lower temperature than that of thermal regeneration. In the present study, the thermal behavior of the monolith during regeneration and the conversion efficiency of NO2 from NO with an integrated exhaust system of a diesel oxidation catalyst (DOC) and DPF have been predicted by one-channel numerical simulation. The simulation results of the DOC, DPF, and integrated DOC-DPF models are compared with experimental data to verify the accuracy of the present model for the integrated DOC and DPF modeling. The effects of catalyst loading inside the DOC and the volume ratio between the DOC and DPF on the pressure drop, the conversion efficiency, and the oxidation rate of PM, have been numerically investigated. The results indicate that the case of the volume ratio of ‘DOC/DPF=1.5’ within the same diameter of both monoliths produced close to the maximum conversion efficiency and oxidation rate of PM. Under the engine operating condition of 175 kW at 2200 rpm, 100% load with a displacement of 8.1, approximately 55 g/ft3 of catalyst (Pt) loading inside the DOC with the active Pt surface of 5.3 m2/gpt was enough to maximize the conversion efficiency and oxidation rate of PM.
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This paper introduces a new model for describing dynamics of a diesel engine aftertreatment system with diesel oxidation catalyst (DOC) and diesel particulate filter (DPF) components for reducing diesel particulate emissions. The system model results in high-index nonlinear differential-algebraic equations (DAEs), which give more general description of the system as compared to ordinary differential equation (ODE) approximations. A singularly perturbed sliding manifold (SPSM) approach is employed for model realization. Simulation results of a soot regeneration sequence show good agreements with that of experimental work. The model will be used for aftertreatment system soot regeneration control applications.
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