0D/1D after-treatment modeling with DARS

Fabian Mauss

www.diganars.com

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• DARS 2.06: New catalyst model

– Description

– Application: Pt-γ-Alumina SCR

– Application: Atom flow analysis

– Coupling to 3D and to 1D engine codes

– Usage with global chemistry

• DARS 2.06: New particulate filter model

– Description

– Results

• Future work

Overview

Reactor network 1D models

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Complete powertrain system - possible now in DARS v2.06:

- New transient 1D models:- Catalytic converter- DPF

- Engine models: DARS SRM for DICI and SI engines- Cooler, pipes and turbocharging 1D models

Species tracked from inlet to exhaust Emission optimization CPU time efficient Tracks inhomogeneities Fuel flexible

Catalyst model

• Usable for:

– Three way catalysts (TWC)

– NOx-storage and reduction catalysts (NSC)

– Diesel oxidation catalysts (DOC)

– Selective catalytic reduction (SCR)

• Catalyst model = 3 model-parameters:

– Heat transfer parameter

– Mass transfer parameter

– Overall reaction efficiency

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Catalyst model

Solution procedure - split into three levels:

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Washcoat

Monolith wall

Channel level

Washcoat level

Heat

conduction

is calculated

Several

representative

channels are

selected for

solving:

• chemistry

• flow

• heat transport

• mass

transport

Detailed

surface or

global

chemistry

Catalyst model

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n-1 n n+1n-2

k-1 k k+1 k+2

p, v, Yi, hg

washcoat

Monolith wall

- Channels are discretized into a number of cells:

- Flow and chemistry calculations are decoupled

- Chemistry calculations are performed in two subsections:

•Bulk gas

•Boundary layer

Catalyst model

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Chemistry calculation• Cell bulk gas = PSR (Gas phase chemistry)

• Heat & mass transfer (bulk gas - thin film layer) - modeled using

heat and mass transfer coefficients

• Thin layer:

• detailed surface chemistry

• global gas phase chemistry

Assumption:• Steady state solution of the flow - in each time step

Catalyst model

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Transient representative channel model,

suitable to model

• Catalyst warm-up

• Hot spots

• Effect of site blocking / poisoning

• Conversion efficiencies

• Non-uniform, non-steady state inlet conditions

• Effect of heat and mass transfer on conversion efficiencies

Catalyst results

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Validation against experiments [Koop & Deutschmann, 2009]

Fröjd, K., Mauss, F. - SAE 2011-01-1306

2500C 4500C

The effect of C3H6 inhibition on NO conversion (steady state, flat-bed reactor)

Catalyst results

The effect of C3H6 inhibition for lean phase, 250 °C

Fröjd, K., Mauss, F. - SAE 2011-01-1306

2011-01-1306

~ 200ppm NO (according to experiment), 0.04% CO, 12% O2, 7% CO2, 10% H2O, balance N2. All measures are by volume. T = 250°C

Catalyst results

The effect of C3H6 inhibition for lean phase, 250 °

Fröjd, K., Mauss, F. - SAE 2011-01-1306

2011-01-1306

Catalyst results

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NO mole fraction and CO site fraction (250 0C) along the catalyst channel, as a function of distance – time

Fröjd, K., Mauss, F. - SAE 2011-01-1306

Catalyst results

NO mole fraction and CO site fraction (250 0C) along the catalyst channel, as a function of distance – time

Response time of 5.5 seconds

2011-01-1306

The effect of C3H6 inhibition for lean phase, 350 °C

Catalyst results – C3H6 inhibition

Fröjd, K., Mauss, F. - SAE 2011-01-1306

Comparison of mole fractions of species in

bulk gas and thin film layer for fuel lean

composition, 90 ppm C3H6, 0.04 % CO.

350°C.

2011-01-1306

H2 acting as reducing agent under fuel rich conditions

Catalyst results

The effect of H2 as reducing agent on NO conversion under steady-state conditions in a flat

bed reactor, comparison of experiments and simulations.

~ 200ppm NO (according to experiment),

60 ppm C3H6, 2.1% CO, 0.9% O2, 7% CO2, 10% H2O, balance N2.

Fröjd, K., Mauss, F. - SAE 2011-01-1306

Catalyst results: atom flow analysis

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Flow paths for nitrogen atoms, fuel rich phase

350 °C, 1% H2 450 °C, 0% H2

[Fröjd, K., Mauss, F. , Investigations of chemical processes in a NOx-storage catalyst by the use of detailed chemistry and flow analysis, ECM 2011, June 2011]

Catalyst results: atom flow analysis

17350 °C, 1% H2 450 °C, 0% H2.

Display limit: 0% of total flux.

Flow paths for oxygen atoms for fuel rich phase. [Fröjd, K., Mauss, F. , Investigations of chemical processes in a NOx-storage catalyst by the use of detailed chemistry and flow analysis, ECM 2011, June 2011]

Catalyst results: atom flow analysis

18350 °C, 1% H2 450 °C, 0% H2

Flow paths for hydrogen atoms for fuel rich phase.

[Fröjd, K., Mauss, F. , Investigations of chemical processes in a NOx-storage catalyst by the use of detailed chemistry and flow analysis, ECM 2011, June 2011]

Coupling to 1D engine code

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Catalyst model in the process to be implemented in DARS interface

for GT-Power 7.0 (DARS ESM).

Kinetic studies (DARS)

- combustion

- in-cylinder emission formation

- catalyst emission reduction

AND

engine performance analysis (GT-Power)

Calculations with global and detailed surface chemistry

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• Global reaction schemes are

invoked via user subroutines

• Detailed Surface Chemistry is

invoked through Read Mechanism in

DARS GUI

Global surface chemistry

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• Global reaction schemes describe the full conversion as one or a few

lumped steps

• Global reaction schemes are tuned for each catalyst type and

morphology

• Inhibition terms used for cross-dependency of reactants

• Cannot take into account transient effects such as storage and poisoning.

C3H6 + 4.5O2 => 3 CO2 + 3 H2O

Detailed surface chemistry

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• Detailed surface chemistry includes all molecular

reaction steps at the surface

• Includes adsorption, reactions at the surface

(Langmuir-Hinshelwood reactions), reactions of gas

phase species with surface species (Eley-Rideal

reactions), desorption.

• Invoked through Read Mechanism in DARS GUI

• Species storage is modeled. Thus transient effects

such as oxygen storage in TWC’s and poisoning can

be modeled.

• Can be combined with global rates for conversion.

• Example: oxygen storage model combined

with global rate for CO, NO and HC conversion

in TWC

NO(s) + Pt(s) <=> N(s) + O(s)

Global reaction rate optimization

1. Define test matrix

1. Isolation of reaction rates: Tuning for CO, HC and NO conversion

separately

2. Combinations representing the possible exhaust gas compositions

3. Temperature ramp for transient conditions / temperature matrix

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0

50

100

150

200

250

300

350

400

450

500

0 200 400 600 800 1000 1200

Te

mp

era

ture

[°C

]

time [s]

T [°C]

Global reaction rate optimization

2. Optimization (e.g. Matlab)

3. Validation for engine cycle

4. Usage: parameter studies

– Effect of catalyst length on

emission conversion

– Effects of exhaust emission

levels on conversion

– Transient crossdependencies

between species.

– Coupling to SRM in-cylinder

model to study overall gain of

in-cylinder parameters (EGR

rate, equivalence ratio, …)

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DARS Catalyst calculation(s)

Outlet concentrations

Evaluation of results

Improved rate parameters

Diesel Particulate Filter (DPF) model

DPF

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DICI-SRM

Reactor level

Porous wall

Channel level

Soot cake

Porous media

and soot cake level

DPF model

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The solution procedure is split into three levels:

Heat

conduction is

calculated

Soot deposition

and oxidation

Solved:

• soot

deposition and

oxidation

• pressure drop

and flow

properties

• chemistry

• heat transport

DPF model

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Porous wall

Soot

cake

Pressure drop and flow between inlet and

outlet channels - modeled by Darcy’s law

Permeability - calculated from the current

level of soot deposited in soot cake and in the

filter

Soot deposition is modeled by unit cell filtration model

Also calculated:• Soot cake growth

• Soot oxidation

• Catalytic reactions in wall

• Heating of wall

• Interaction between soot cake and catalytic reaction paths

• Heat conduction throughout the filter

DPF model

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[Konstandopoulos, A.G. et al., SAE 2000-01-1016]

DPF results

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Flow velocities and pressure in the DPF channel

DPF results

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Filter wall permeability and collection efficiency

Future work

• Currently coupling to STAR

• Currently coupling to GT-Power

• Built-in setup for different catalyst types

– TWC (chemistry available)

– DOC (Pt-γ-Alumina chemistry available)

– SCR

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