ic engines modeling

7/31/2019 IC Engines Modeling

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MODELING THE UNSTEADYFLOWS IN I.C. ENGINE PIPE

SYSTEMS BY MEANS OF AQUASI-3D APPROACH

G. Montenegro, A. Della Torre, T. Cerri, A. Onorati

Department of Energy, Politecnico di Milano, Milan, Italy


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Outline

A. Della Torre Paper Number: ICES2012-81181

Motivation and scope

Description of the approach:

Governing equations

Numerical structure and limiting technique

Specialization for the modeling of specific devices

Validation: high performance Aprilia V4 engine:

Pressure pulses in the intake and exhaust ducts

Volumetric EfficiencySound Pressure level


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Motivations and scope


1D simulation codes are well-established and reliable tools but ...

Corrective lengths and equivalent 1D duct schemes for 3D components

Equivalent duct schemes are not a-priori known

The optimization of the layout of 3D components is not possible


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Quasi-3D approach


Geometry is reconstructed by

means of a network of cells and

ports

The main characteristic lengths in

the space are reconstructed


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Governing equations


Based on the formulation of the conservation equations of mass, momentumand energy for unsteady flows

t

+ (U) = 0

U

t+ (UU) = p

e0

t + (e0U) + (pU) = 0

Viscosity of the gas, both in the intake and exhaust system, is very low: it can

be neglected without introducing an excessive approximation (Euler formula-tion)

System of equations is closed with the perfect gas equation of state


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Numerical Method


Second order accurate and stable

Pseudo-staggered grid:

Mass and Energy equations are integrated over the cell control volume

Momentum equation is integrated over the port control volume

The method is stabilized adding a diffusion source term to the momen-

tum equation

cell CV port CV


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Time marching procedure


PORT

CELL

Shock-tube test case

0 0.2 0.4 0.6 0.8 1x [m]

1

2

3

4

5

Pressure

[bar

]

exactDTM

(b)

Explicit time marching method

Staggered leapfrog method applied to a staggered grid arrangement

Spatial second order accuracy in the resolution of the pressure discontinuities


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Model specialization


Cell and port definitions have been specialized to handle particular devicessuch as:

Catalysts (TWC, DOC, SCR ...)

Diesel Particulate Filters

Perforated elements (baffles, pipes)

Filtering devices

Sound absorbing material


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Perforated Elements


Perforates are modeled by extending the properties of the port element

The perforated port is characterized by the number of holes nh, hole cross

section Ah, hole length lh and by the total port surface Ac

The momentum equation is solved only for one single hole and applied to allholes


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Filter cartridge


Ms = (pDarcy)Apt

LpDarcy =

wwall

KwallUp

Cartridge modeled as a porous media: Darcys law

Thickness of the layer is modeled but not captured by the mesh


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After-treatment device: catalyst


single channel 3Dcell

monolith macro cells

external 3Dcell external 3Dcell

w

Macro cell: it contains only a representative channel

1D flow solved in the channel and extended to the others belonging to the

same macro cellGas-wall friction (Churchill)

Vena contractaMs = (UF) |U| fw

2

t + pinoutF

t

L


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Test Case: Aprilia V4 engine


Air-box and silencer exibit a complex geometry

1D-quasi3D model is based on pure geometrical dimensions

Engine Type Spark Ignition

Number of cylinder 4-V65o

Total displacement 999.6 x 10-6 [m3]Bore 0.078 [m]

Stroke 0.0523 [m]

Compression ratio 13:1

Number of valves per cylinder 4

Air Management Naturally aspirated

Injection system PFI


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1D-quasi3D integrated model


Fully coupled simulation with 1D code (GASDYN)

The same numerical method is applied to 1D pipes and 3D components


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Air-box and silencer modeling


Main characteristic lengths are captured

Number of elements: 1634 cells for the air-box, 2934 cells for the silencer

Average mesh spacing is 1.5 - 2 cm


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Intake trumpets in a close-coupled

configuration

Interference between the different

cylinders

Wave motion in the air-box strongly

affects the volumetric efficiency

Complex internal layout

Flow reversal, perforates, catalystmonolith, internal pipes

Back-pressure & radiated noise pre-

diction


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Intake trumpets in a close-coupled

configuration

Interference between the different

cylinders

Wave motion in the air-box strongly

affects the volumetric efficiency

Complex internal layout

Flow reversal, perforates, catalystmonolith, internal pipes

Back-pressure & radiated noise pre-

diction


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Validation: pression pulses on the intake


Pressure pulses in three differ-ent locations

Pulses in the intake runners

are strongly influenced by theinterference between the cylin-

ders

Cylinder 1 : 6500 rpm

-360 -300 -240 -180 -120 -60 0 60 120 180 240 300 360Crank angle [o]

0.70

0.80

0.90

1.00

1.10

1.20

1.30

Pressure[Pa

x105]

Measured

1D-quasi3D


-360 -300 -240 -180 -120 -60 0 60 120 180 240 300 360Crank angle [o]

0.70

0.80

0.90

1.00

1.10

1.20

1.30

Pressure[Pa

x105]

Measured

1D-quasi3D


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Validation: pression pulses on the intake



-360 -300 -240 -180 -120 -60 0 60 120 180 240 300 360

Crank angle [o]

0.70

0.80

0.90

1.00

1.10

1.20

1.30

Pressure[Pax105]

Measured

1D-quasi3D


-360 -300 -240 -180 -120 -60 0 60 120 180 240 300 360

Crank angle [o]

0.70

0.80

0.90

1.00

1.10

1.20

1.30

Pressure[Pax105]

Measured

1D-quasi3D


-360 -300 -240 -180 -120 -60 0 60 120 180 240 300 360

Crank angle [o]

0.60

0.75

0.90

1.05

1.20

1.35

1.50

Pressure[Pax105]

Measured

1D-quasi3D


-360 -300 -240 -180 -120 -60 0 60 120 180 240 300 360

Crank angle [o]

0.60

0.75

0.90

1.05

1.20

1.35

1.50

Pressure[Pax105]

Measured

1D-quasi3D


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Validation: pression pulses on the exhaust


Pressure pulses are gauged downstream of cylin-

der 4

Strong influence of the 4 in 2

in 1 junction on the exhaustline


-360 -300 -240 -180 -120 -60 0 60 120 180 240 300 360Crank angle [

o]

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

2.00

Pressure[Pax

105]

Measured

1D-quasi3D


-360 -300 -240 -180 -120 -60 0 60 120 180 240 300 360Crank angle [

o]

0.60

0.90

1.20

1.50

1.80

2.10

2.40

Pressure[Pax

105]

Measured

1D-quasi3D

V l i ffi i d b k


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Volumetric efficiency and back-pressure


Modeling is based on pure geometrical reconstruction

The quasi3D model allows to investigate the effects of a geometry change

(e.g. air-box internal layout) on the overall engine performances

Optimization of the geometry and the properties of internal devices (perfo-

rates, filtering elements, catalyst)

Volumetric Efficiency

4000 5000 6000 7000 8000 9000 10000 11000 12000 13000Engine speed [rpm]

0.3

0.4

0.6

0.8

0.9

1.1

1.2

Volumetricefficiency/Vmax[-] Measured

1D-3Dcell

Back Pressure

4000 5000 6000 7000 8000 9000 10000 11000 12000 13000Engine speed [rpm]

0.90

1.00

1.10

1.20

1.30

1.40

1.50

Pressure[P

ax105]

Measured

1D-3Dcell

S d l l l l ti


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Sound pressure level calculation


Prediction of the acoustic behaviour of the silencing device in real operatingconditions

Optimization of internal layout of mufflers

Effects on both acoustics and performances

0 1000 2000 3000 4000 5000 6000Frequency [Hz]

0

25

50

75

100

125

150

175

SoundPressureLevel[dB]

Without silencer

With silencer

O ti i ti


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Optimization


Example: maximization of silencer TL

Parameters: position of the two internal baffles

Other possible targets:

Stand-alone component: TL & pressure drop

Entire engine: SPL & volumetric efficiency

O ti i ti


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Optimization


Example: maximization of silencer TL

Parameters: position of the two internal baffles

Other possible targets:

Stand-alone component: TL & pressure drop

Entire engine: SPL & volumetric efficiency

Computational runtime and accuracy


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Computational runtime and accuracy


Results comparable to 1D-3D simulations

Computational run-time 2-3 times that of a 1D simulation

The increase of computational runtime compared to 1D is justified by theenhanced predictivity


-360 -300 -240 -180 -120 -60 0 60 120 180 240 300 360

Crank angle [o]

0.40

0.60

0.80

1.00

1.20

1.40

1.60

Pressure[Pax105]

Measured

1D 3D coupling

1D-quasi3D Computational runtimes

1D 15 [min]

1D-3D 20 [hours]1D-quasi3D 45 [min]

Conclusions


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Conclusions


A stable numerical procedure to perform both acoustic and fluid dynamic sim-ulation of 3D shaped devices has been presented

Specific sub-models for filtering and after treatment devices have been de-

veloped

Engine modeling is based on pure geometrical reconstruction without the

need of resorting to corrective lengths or equivalent ducts schemes

Engine performance parameters can be determined with good accuracy and

low computational effort

Acoustic properties can be evaluated in real operating conditions

DOE shape optimization is affordable


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Thank you for your attention!

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