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The majority of Diesel exhaust gas aftertreatment system design and development work is done experimentally by means of long and expensive engine bench tests. The final system configuration is generally the product of a series of experimental “trial and error” operations. In order to shorten the development process, to reduce testing costs and to increase the durability of Diesel Particulate Filters (DPFs), multidisciplinary simulation tools are needed to predict possible failures of the DPF. Recently, several numerical models have been developed to simulate globally the soot loading capacity, the pressure drop evolution and the regeneration behaviour in ceramic wall-flow filters. Less effort has been devoted to the development of dedicated models for the simulation of the microstructural flow phenomena and thermo-mechanical behaviour of the filters. This paper describes the development of a multi-physics software tool based on OpenFOAM embedded in the DexaSIM Graphical User Interface (GUI) which is able to handle the evolution of microstructural material properties and complex physical phenomena inside the filter material as well as response of complete filters under engine operating conditions. The modelling approach hence builds on the multiscale link between microstructural evolution and specific macroscopic exhaust system features with the objective to achieve major improvements in material design and lifecycle assessment.
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OpenFOAM .International Conference 2007OpenFOAM .International Conference 2007
A Multiscale Simulation Approach for Diesel Particulate A Multiscale Simulation Approach for Diesel Particulate Filter (DPF) Design Based on OpenFOAM and DexaSIMFilter (DPF) Design Based on OpenFOAM and DexaSIM
Johannes Johannes LeixneringLeixnering, Bernhard Gschaider, ICE Strömungsforschung GmbH, Bernhard Gschaider, ICE Strömungsforschung GmbHWilhelm Brandstätter, Wilhelm Brandstätter, RiesRies Bouwman, Montanuniversität LeobenBouwman, Montanuniversität Leoben
IntroductionIntroduction
IntroductionIntroductionDiesel Particulate Filters (DPF) – Past and PresentMultiscale Simulations
• OpenFOAM• DexaSIM
Material reconstruction on a microscopic scaleMaterial reconstruction on a microscopic scaleIsotropic Material Reconstruction method (IMR)Anisotropic Material Reconstruction method (AMR)
Microscopic SimulationsMicroscopic SimulationsPorous structuresDetermination of Porosity and PermeabilitySoot deposition
Macroscopic SimulationsMacroscopic SimulationsExhaust systemOverall properties
ConclusionsConclusions
Diesel Particulate Filters (DPF)Diesel Particulate Filters (DPF) 1/41/4
DPF FiltersDPF FiltersGood solution to abate particulate matter (PM) quantity
to the required limits (EURO IV)The innovation in this field is not yet finished
• Imposed limits evolve (EURO V)• Different combustion products (particle dimension, density,
etc.) due to the introduction of new Combustion conceptsDifficult to study in detail
• Experiments with destructive tests (burning, cutting …)• Simulations of global parameters with submodels. No direct
simulation of porous structure• No connection between microstructures and macroscopic
material properties
DPFDPF 2/42/4
Experimental research and development (R&D)Experimental research and development (R&D)Trial and errorThe filter material is difficult to investigate in detail
• No detailed information on the soot deposition• No detailed information on the heat transfer
Deeper insight required into chemical and physical Deeper insight required into chemical and physical phenomena in phenomena in DPFsDPFsDuring filter regeneration Shorten the development processIncrease the durability of DPFs
Multiscale simulation tools are needed to predict possible Multiscale simulation tools are needed to predict possible failures of the DPFfailures of the DPF
DPF DPF –– PastPast 3/43/4
ToolsToolsTest bench
• Expensive• Only overall information
Commercial CFD tools• Unflexible• Experts• High costs
NeedsNeedsFast and accurate methods for DPF
design to meet Euro V legislation• Euro V, Euro VI ...
DPF DPF –– PresentPresent 4/44/4
New approachNew approachMultiscale simulations
• Detailed study of microscopic heterogene porous structures• Influence of porous structure on macroscopic homogene filter
OpenSource software• Flexible• Low costs
NeedsNeedsTools to easily reconstruct porous structuresTools to study connection between microscopic
improvements on overall performance
Multiscale Simulations Multiscale Simulations -- Past Past 1/21/2
MacroscopicMacroscopic1D and 3D Simulations of filters (wall flow, foam …)Homogeneous porosities Measured permeabilities
• are used to model the effect of filter material on the exhaust gas flow
Without extensive experimental calibration the predictive capability of these models proved to be limited
MicroscopicMicroscopicLattice-Boltzmann-Method (LBM)
• Cold flow and particle deposition in porous media • No heat transfer and chemical surface reactions
1D 1D –– 3D coupling3D couplingTo improve calculation time
Multiscale Simulations Multiscale Simulations -- Present Present 2/22/2
Multiscale approachMultiscale approachGeneration of 3D computational
microscopic and macroscopic geometry• Based on Computer Tomography (CT)
image and DexaSIMMicroFOAM
• OpenFOAM based solver to study microscopic porous structures
MacroFOAM• OpenFOAM based solver to study
complete exhaust systems• Material properties calculated in
MicroFOAM are used to define overall properties
Multiscale Simulations Multiscale Simulations -- Present Present 2/22/2
DexaSIM DexaSIM -- preprocessorpreprocessor
Catalyst:
Chemical reactions? Efficiency?
Soot filter:
Loading? Structure?
Porosity, permeability in time?Inlet:
Temp, pressure, species
Outlet:
Species? Temperature?
Pipeline:
Pressure drop? Turbulence?
OpenFOAM OpenFOAM -- solversolver
OpenFoamOpenFoamAdvantages
• OpenSource• C++• Very flexible • Direct implementation of physics and mathematics
Disadvantages• Not easy to use (for beginners)
GUIGUIDexaSIM is preprocessor and GUI for exhaust gas
aftertreatment simulations• Multi platform
LinkLinkhttp://www.ice-sf.at/dexasim_download.shtml
ParaView ParaView -- postprocessorpostprocessor
ParaviewParaviewOpenSource
• Very flexible• Multi platform
LinkLinkhttp://www.paraview.org/New/index.html
Modelling on a Microscopic ScaleModelling on a Microscopic Scale
DexaSIM DexaSIM Reconstruction of 3D material samples from 2D
Computer Tomography Image Statistical functions are used to characterise material
samples• pore diameter distribution• pore distance autocorrelations• lineal path functions, etc.) material samples are
mathematically characterised.
Setup of complete exhaust geometry and boundary conditions
Material reconstructionMaterial reconstruction 1/21/2
Isotropic material reconstruction methodIsotropic material reconstruction method1. Obtaining a 2D CT image of the material2. Converting the CT image to a digitised image3. Retrieving statistical parameters from the digitised
image4. Reconstruct 3D digital model or mesh according to
statistical parameters
Material reconstructionMaterial reconstruction 2/22/2
Anisotropic material reconstruction method Anisotropic material reconstruction method 1. Obtain 2D grey-scale images of the material2. Combine 2D images to one 3D grey-scale image3. Digitise and reconstruct the 3D digital model or
mesh
Microscopic Simulations Microscopic Simulations 1/61/6
Equi-distant Cartesian mesh
porosity 0.77
Body Fitted (SPIDER) mesh
porosity 0.89 (350K) and 0.81 (1500K)
Microscopic Simulations Microscopic Simulations 2/62/6
Microscopic Simulations Microscopic Simulations 3/63/6
Microscopic Simulations Microscopic Simulations 4/64/6
Soot deposition at the pore wallsSoot deposition at the pore wallsTransport equation
Depot ratio D
0=+∇⋅∇−⋅∇+∂
∂sootsootsoot
soot SKut
ρρρ
sootdepsoot RS αρ=
0=−∂
∂soot
dep St
ρ
solid
fluid
D=0.2
A
solid
fluid
V
Aα = A/V
solid
fluid
D=1
C
solid
fluid
D=0.5
B
solid
fluid
D
Microscopic Simulations Microscopic Simulations 5/65/6
Microscopic Simulations Microscopic Simulations 6/66/6
Filter 1: Continuous Regeneration Trap (CRT)Filter 1: Continuous Regeneration Trap (CRT)
Filter 2: Passive soot trapFilter 2: Passive soot trap
Macroscopic SimulationsMacroscopic Simulations 1/21/2
Oxidation of CO and NO
Passive soot trap
22
22262
22
2226472
22
CONCONOOHCOOHC
COOCO
+→++→+
→+
Macroscopic SimulationsMacroscopic Simulations 2/22/2
CO2
Temperature
ConclusionConclusion
A complete method has been presented to study filter materials oA complete method has been presented to study filter materials on a n a microscopic level to see the influence of microscopic R&D on themicroscopic level to see the influence of microscopic R&D on themacroscopic filter behaviourmacroscopic filter behaviour
Multiscale LinkMultiscale LinkInfluence of microstructural evolution on macroscopic features Objective: achieve major improvements in porous material design
OpenFOAM OpenFOAM Combines microscopic and macroscopic scale simulations in one tool
• e.g. DexaSIM. Validations of the simulations with experimental results look promising
OutlookOutlookExtensive experimental validating of the modelsImplementation of sub models for
• wall flow filter (anisotropic approach) • thermal activity inside the filter material (Tension, cracking, fluid-structure
coupling ...)
