Fundamental and Applied Studies for Internal Combustion ...powerlab.fsb.hr/ped/kturbo/OpenFOAM/Berlin2008/SessionVA/OSCIC … · • Piaggio Quasar 250 Compr. ratio ~ 11 Stroke 60

POLITECNICO DI MILANO Department of Energy

Gianluca D’Errico Open Source CFD International Conference 2008

Fundamental and Applied Studies for Internal Combustion Engine

Simulations by OpenFOAM

G. D'Errico, G.Montenegro, T.Lucchini, F.Piscaglia

Department of Energy, Politecnico di Milano

http://www.engines.polimi.it



An opensource CFD platform, OpenFOAM® :• to implement different models into the same code• to allow collaborative studies• to be applied for industrial applications

Objectives:Fundamental studies: to improve the understanding of the occurring physical and chemical process

Applied research: to provide computational tools which can help the designer in the development of future engines.

Tool:



Fundamental studies Applied research

RANS Combustion

Spray models

Chemistry models

Mesh motion

Acoustics

Alternative fuels

DPF

1D-3D coupling

In-cylinder SI engine simulation

In-cylinder Diesel engine simulation

Whole engine system simulation

Engine component design



Diesel Combustion modeling

Simplified chemistry (4 species)

Tabulated ignition delays

Reliable and fast

Industrial applications

TITC(Tabulated Ignition Turbulent Combustion)

Complex chemistry

ISAT algorithm

Computationally demanding

Diagnostic purposes

PSR (Perfectly Stirred Reactor)

Implementation of two different combustion models



SANDIA combustion chamberFundamental validation

• ¼ vessel volume• 50000 cells• Mesh size:

liquid spray region:1 mmdownstream of the liquid spray

penetration: 0.5 mmmaximum mesh size: 4 mm



Computed vs experimental equivalence ratio distribution at auto-ignition time

x = 20 mm, t = 0.7 ms

x = 30 mm, t = 0.7 ms



6 cases;O2 from 10% to 21%Tamb from 750 to 1300

Liu et al. (Comb. Flame, vol 137) 44 species, 112 reactionsIt contains acetylene chemistry

The PSR model is able to reproduceboth premixed and mixing-controlledcombustion

Overprediction of the ignition delay

Poor comparison for low temperature



Formaldehyde and PAH distributionsModerate soot conditions (T = 1000K, O2 = 21%)

• Formaldehyde (HCHO) formation close to the lift-off length. No separation between HCHO consumption and PAH formation

(SAE 2006-01-3434)

Low soot conditions (T = 900K, O2 = 21%)

• Formaldehyde (HCHO) formation upstream the lift-off length. Separation between HCHO consumption and PAH formation



Full Diesel engine cycle simulationFull Diesel engine cycle simulation

-- 1D1D--3D Coupling with i3D Coupling with intakentake strokestroke-- oneone sectorsector compressioncompression--combustioncombustion

5Injector holes

2.6Swirl ratio

1.2 mmSquish height

-131 deg TDCIVC

10600 cm3Total displacement

14Compression Ratio

134 mmStroke

127 mmBore

6Cylinders

SEATEK 850 PlusType



Intake stroke in a Diesel engineFourteen grids were used tocover the whole intake stroke

The grid is unstructuredcomposed by hexahedra, prisms and tetrahedra. Hexahedral cells are used in the valve region to follow the incoming flow field



Mesh motion – Compression stroke

Dynamic mesh layering : a set of user-defined, horizontal cells removeslayers of cells according to specified maximum and minimum thickness values

Start of injection



Mesh motion – Injection and combustion

• Mesh keeps the spray-orientation• User defined faces for dynamic mesh layering• User defined bowl points moving with piston velocity



In-cylinder pressure, temperature and soot

13 CAD ATDC

5 CAD ATDC

0 CAD ATDC

Temperature Soot



SANDIA Optical Engine: experimental apparatusTwo different bowl configurations tested

70% bowl

80% bowl



Fuel spray evolution1 CAD 2 CAD 3 CAD

4 CAD 7 CAD 8 CAD



Validation: non reacting case – 70% bowl – 12 ºATDC

• Influence of swirl on the fuel distribution

• Good agreement of equivalence ratio distribution on the cut planes 1 and 2

• Result on the cut plane 3 to be improved

Equivalence ratio distribution:

Cut

1C

ut 2

Cut

3



Validation: non reacting case – 80% bowl – 12 ºATDCEquivalence ratio distribution:

Cut

1C

ut 2

Cut

3

• Influence of the bowl shape on the equivalence ratio distribution well captured

• Maximum equivalence ratio values slightly overpredicted



Current work: flame structure validation (70% bowl)

OHHCHO + PAH

11 ATDC,Cut 1

14 ATDC,Cut 1

HCHO + PAH OHExperimental

Preliminary results



GDI Engine Simulation• Assessment of the Weller+EDM combustion model at engine conditions

• Mitsubishi-IFP GDI Engine test case

Complex geometry

• Simulation of the intake + compression + injection + combustion phases

0 CAIVO

133.5 mmRod length

211 CAIVC

89 mmStroke81 mmBore

• Mesh deformation close to TDC to control the grid quality close to the valves•After 90° TDC use of dynamic layering close to the piston• 9 meshes for the whole intake stroke



Fuel injection phase – fuel vapor distribution

-50° TDC -40° TDC -22.5° TDC (spark timing)

-15° TDC -5° TDC 20° TDC

Combustion process – distribution of b



Intake stroke investigation in spark ignition engines

• Piaggio Quasar 250

~ 11Compr. ratio

60 mmStroke72 mmBore

Sliding interface and dynamic mesh layering on canted valves



1D-3D couplingAt the OpenFOAM International Conference 2007 we presented a strong coupling strategy between GASDYN and OpenFOAM

The Riemann problem is solved locally for each face constituting the domain interface. It allows to treat flow non-uniformities.

This approach was further validated and integrated in GT-Power, in collaboration with GAMMA Technologies Inc.

Available applications:• Closed valve cylinder modeling (Diesel and S.I.)• Intake and exhaust systems modeling




• Values are passed from GT-Power to OpenFOAM at the beginning of the 3D simulation:

• Initial pressure• Initial temperature• Initial swirl and tumble coefficient• Initial turbulence level• EGR, fuel, products and oxidant mass fractions

• Other parameters, such as injection law, IVC,EVO and others, are set recurring to standard OpenFOAMdictionaries

• Istantaneous values of pressure, temperature, turbulence and mass fraction of EGR, products, oxidant and fuel are passed back to GT-Power at each time step

Cylinder coupling




• OpenFOAM can follow the time step given by the 1D model or it can perform subcycling according to the Courant number required by the 3D




• Values are passed from GT-Power to OpenFOAM at each time. 1D values can be assigned uniformly at the interface

• A coupling procedure based on the solution of the Riemann problem allows to assign non uniform fields compatible with the 3D solution

• Transport of chemical species will be implementedto track different gas compositions such as EGR inside of intake systems

Duct system coupling



Full Scale DPF Modeling in OpenFOAM®

OUTLINE•Development of a NEW STEADY COMPRESSIBLE SOLVER FOR FLOW

THROUGH THIN POROUS LAYERS: rhoSimplePorous1DFoam

TO BEGIN WITH:•OpenFOAM ® built-in steady compressible solver rhoPorousSimpleFoam®

MOTIVATION:• Need to have a predictive tool for real world Diesel Particulate Filter design

(segmented filters, non axis-symmetric geometries) in internal combustion engine simulation;

• Channel-scale simulation cannot provide a detailed description of radialtemperature distribution;

• Simulation of thermal gradients occurring during filter-regeneration, due to non-uniform inlet flow conditions (HEAT TRANSFER PROBLEM);



rhoPorousSimpleFoam®:Despite the approach based on POROUS VOLUME TERM (rhoPorousSimpleFoam®) is

reliable for most applications, it may not be convenient as diesel exhaust after-treatment simulations are performed

• mesh generation (in particular the definition of porous regions) is not straight-forward• DPF channel section is discretized in a high number of cells• the resulting fine grid and the small size of porous cells (about 10−4 m) cause low

simulation time-steps HIGH COMPUTATIONAL TIME• friction between the flow and the porous wall is not accounted

Axial component of the flow INSIDE porous medium in Diesel Particulate Filters is negligible

Corning EX-80 2.66”x4.5” 100/17



• Each channel is discretized by a series of CV along the axial direction. Cell size over the transverse direction is taken equal to the channel size: 1D schematization of filter channels;

• Porosity has been set as a cell-face property the orientation of the porous surface with respect to the reference axes has no influence;

• Friction between fluid and porous walls has been modeled as an (axial) implicit volume sink term;

• Fully automatic setup of open/closed pattern: new utility createDpfPatch.• Straightforward mesh generation of the filter (“porous” property automatically set);• Easier definition of the whole layout;• Faster simulations, because a more efficient numerical solver may be used

New Solver rhoSimplePorous1DFoam for Porous Media



• The method mimics the operation of a solution procedure devised for a staggered variable arrangement, but keeping the colocated variables;

• Momentum equation is solved for the face flux φ instead of cell-centered velocity U;

• Face velocities uf are calculated from the corrected flux fields; • The cell-centered velocity is merely regarded as a secondary variable, which is used in the construction of the momentum equation;

• Pressure gradient is also calculated on cell faces.

New Solver rhoSimplePorous1DFoam for Porous Media



The three-dimensional mesh geometry of the monolith is generated from a 2D sketch; faceSetscustomization for DPF applications is performed by an automatic algorithm (createDpfFaceSets):

inlet and outlet ends of the monolith show a typical “chessboard”arrangement, where channels are alternatively open and closed; cell faces representing the closed-ends of filter channels are automaticallyset as ”walls”

plug ends are automatically generated by extruding inlet and outlet ends of the monolith and then adding the resulting mesh to the original one; they have non-permeable walls, that are automatically grouped and set as ”walls”

porosity is modeled as a cell-face property; porous walls dividing inlet and outlet channels of the monolith are grouped in a faceSetdefined as ”porous”

The solid region for the DPF material and the cement strips is used to model the heat exchange to the surroundings

Case Setup



Validation of the rhoSimple1DExpFoam solver (IBIDEN SD031 test brick)

Test case:• 34.24 x 34.24 x 142.4 mm brick;• 288 channel pairs;• Cold flow;• 198144 hexahedral cells;• 160080 porous faces.

Test case:• 34.24 x 34.24 x 142.4 mm brick;• 288 channel pairs;• Cold flow;• 198144 hexahedral cells;• 160080 porous faces.



VELOCITY FIELD

PRESSURE FIELD

Validation of the rhoSimple1DExpFoam solver (IBIDEN SD031 test brick)

Documents

Fundamental and Applied Studies for Internal Combustion ...powerlab.fsb.hr/ped/kturbo/OpenFOAM/Berlin2008/SessionVA/OSCIC … · • Piaggio Quasar 250 Compr. ratio ~ 11 Stroke 60