DARS

FUEL MODEL DEVELOPMENT

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DARS Products (names valid since October 2012)

DARS

0D & 1D tools

Old name: DARS Basic

Stand alone tool for 0D-1D analyses of chemical processes in industrial and scientific devices

DARS

Reactive Flow Models

tools for 3D/ CFD

calculations

- Chemistry module coupled to CFD (STAR-CD and STAR-CCM+)

- Gas phase chemistry and surface chemistry

- TIF: Transient interactive flamelet model coupled to STAR-CD

DARS Fuel

New!

Advanced fuel models

- Libraries and run-time reaction mechanisms for detailed chemistry modeling in conjunction with DARS CFD/TIF

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DARS (Basic)

Reactors

Homogeneous

CV

CP

PSR

RCM

SRM

(Stochastic Reactor Models)

PSR

SRM-HCCI

SRM-Diesel

SRM SI

DARS

1D Models

Piping

Coolers

After-treatment

Catalytic Converter

Particulate Filter (DPF)

Turbo charging

Flames

Burner stabilized

Freely propagating

Counter Flow

Flamelet

Chemical Mechanisms

Development

Analysis

Reduction

EXAMPLE FOR FUEL MODEL DEVELOPMENT WITH DARS

Outline

• Ethanol-gasoline blend selection

• Ethanol-gasoline chemical mechanism

• DARS mechanism analysis – Sensitivity analysis

– Flow analysis

– Necessity analysis

– Life time analysis

• DARS mechanism reduction

• Ethanol-gasoline dual fuel table generation

ETHANOL-GASOLINE BLEND SELECTION

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Aspects of surrogate fuel choice

• Real fuels are not consisting of one single component

• The surrogate chemistry needs to be representative of the components present in the real fuel

• Physical properties and chemical properties need to be matched

• Example: ethanol-gasoline fuel mixture

– Standards: DIN EN 228, SS155422

– E5/E10: unleaded gasoline with 5/10% ethanol

– E75/85: Winter/summer mixture containing 75/85% ethanol

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Gasoline E5 E10 E75 E85

RON 95* 95-98 95-98 101-104**

99-102**

Density (kg/m3) - 750 754 775 785

Aromatic content (%v/v) - 35.0 - - -

Lower heating value (MJ/kg):

- 41.8-43.8

40.9 30.2 29.2

Note: * The base gasoline used for mixing might be of varying quality for different mixtures ** Reported octane numbers for E75/85 are approximations

Methodology

• Find a base gasoline composition which conforms to aromatic content, as well as density, lower heating value and RON when mixed with 5% ethanol.

• RON calculations:

– Modified Linear by Volume (MLbV) [1]: Good approximation for synergetic blending of iso-octane, n-heptane and toluene.

– Linear by Mole Fraction (LbMF) [2]: Shown to yield good results for gasoline/ethanol blends.

• Calculate RON for the gasoline based on the MLbV method, and the effect of the added ethanol by the LbMF method.

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Calculated liquid volume fraction

Calculated gaseous mole fraction

A1CH3 0.33684 0.45482

I-C8H18 0.50688 0.39753

N-C7H16 0.15628 0.14765

Ethanol-gasoline fuel mixture – properties

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740 745 750 755 760 765 770 775 780 785 790 795

0 20 40 60 80 100

Den

sity

(kg

/m3

)

% Ethanol (vol.)

Calculated mixture

Reference data

28

30

32

34

36

38

40

42

44

0 20 40 60 80 100

Low

er h

eati

ng

valu

e (M

J/kg

)

% Ethanol (vol.)

Calculated mixture

Reference data (min)

Reference data (max)

94

96

98

100

102

104

106

108

110

112

114

0 20 40 60 80 100

RO

N

% Ethanol (vol.)

Calculated mixture

Reference data (min)

Reference data (max)

Estimate from simple correlation (PREEM)

0

200000

400000

600000

800000

1000000

1200000

200 300 400 500 600

Hea

t o

f va

po

riza

tio

n [

J/kg

]

Temperature [K]

Gasoline

Ethanol

Two components considered for preferential evaporation

ETHANOL/GASOLINE MECHANISM

Ethanol-gasoline mechanism

• C1 to C4 chemistry extensive validated

• Single fuel components validated against a wide range of experiments, such as flames, shock tubes, flow reactors, …

• Sub models for NOx chemistry and soot formation

• Detailed mechanism around 480 species, reduced around 250 species

Mechanism analysis

Sensitivity analysis

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Reaction r sensitivity with respect to reaction R:

Species s sensitivity with respect to species j:

Variable Y can be: mass fraction of a target species, or temperature of the gas.

kOCHR ]][[ 24

RT

E

na

eTAk

normalized and ranked

of a certain reaction R

Flow analysis

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Analyses the flow of atoms between species

Atoms fluxes [mol/cm3/sec]

H atom O atom

Graphs are drawn for given limits of the flux (low values of limits give very

branched praphs).

Necessity analysis

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A combination of sensitivity and flow analysis

Life time analysis

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Measures the rate of consumption of a species

Mechanism reduction

Use the specific Reduce Mechanism module:

Reduce the mechanism

Remove redundant species according to:

- preset criteria (as the necessity level, calculated within the previous mechanism-analysis step)

OR

- ad-hoc criteria

Reduce the mechanism

• You can export your reduced mechanism

• You can reduce your mechanism in several steps

Options for reduced mechanism

Compare the results obtained with the original vs. the reduced mechanism

In this example: the reduced mechanism gives slightly slower ignition compared to the original mechanism, with a difference of only 2%.

However, the gain in computational time is approximately 90% for this reduced mechanism case.

Analyze reduced mechanisms results

User friendly post-processing interface

ETHANOL-GASOLINE DUAL FUEL TABLE GENERATION

Table generation process

Table generation process

Table generation process

Table generation process

Flame sp

eed

DARS-FUEL tabulated chemistry library

• ECFM-3Z-TKI • Laminar flame speed

• Soot/NOx source terms

ECFM-3Z-TKI tables

ECFM-3Z-TKI Progress variable solver

• Pressure: 40 bar, Tunb: 800 K, Z: 6.22e-2, PRF 95

ECFM-3Z-TKI Tables

• Single fuel table (PRF 95) – Temperature: 101 points between 600 K and 1600 K – Pressure: 8 points between 10 bar and 80 bar – Mixture fraction points: 6 points depending on stoichiometry – EGR points: 5 values between 0 % and 90 % EGR – Temperature segregation: 21 values between 0 and 1 – Around 60 MB data

• Dual fuel table (ethanol-gasoline mixtures) – Temperature: 41 points between 600 K and 1600 K – Pressure: 11 points between 10 bar and 200 bar – Mixture fraction points: 16 points depending on stoichiometry – EGR points: 5 values between 0 % and 90 % EGR – Temperature segregation: 21 values between 0 and 1 – Fuel composition points: 11 values between 0 and 1 (mass fraction ethanol) – Around 400 MB data

Laminar Flame Speed Tables

• Single fuel table (PRF 95) – 0.2 ≤ Φ ≤ 4.0 [-] – 300 ≤ Autoignition T [K] – 1 ≤ P ≤ 130 [bar] – 0 ≤ EGR ≤ 50 [%] – laminar flame speed above 1 cm/s

• Dual fuel table (ethanol-gasoline mixtures) – 0.2 ≤ Φ ≤ 4.0 [-] – 300 ≤ Autoignition T [K] – 1 ≤ P ≤ 130 [bar] – 0 ≤ EGR ≤ 50 [%] – laminar flame speed above 1 cm/s – Ethanol/gasoline fuel fraction 0-1

0

20

40

60

80

100

0 0.5 1 1.5 2 2.5 3 3.5 4

LFS

[cm

/se

c]

Equivalence ratio

Soot/NOx tables

• Single fuel table (PRF 95) – Flamelet oxidizer temperature: 300 – 1200 K in steps of 100 K – Logarithmic stepping, 1 – 200 bar, 9 points – Mixture fraction points: 0-1, 101 points – EGR points: 11 values between 0 % and 50 % EGR – Scalar dissipation rate points: 0 – extinction [1/s]

• Dual fuel table (ethanol-gasoline mixtures) – Flamelet oxidizer temperature: 300 – 1200 K in steps of 100 K – Logarithmic stepping, 1 – 200 bar, 9 points – Mixture fraction points: 0-1, 101 points – EGR points: 11 values between 0 % and 50 % EGR – Scalar dissipation rate points: 0 – extinction [1/s] – Fuel composition points: 11 values between 0 and 1 (mass fraction ethanol)

DARS Fuel

Accurate reaction schemes – ready to use! – Plug in to STAR-CD, STAR-CCM+,

DARS-TIF – No additional work needed

Free basic mechanism for TIF/PVM – Diesel – Gasoline – Requires a DARS license

Free basic libraries for ECFM

– Diesel – Gasoline

Other fuels are available as library on license base

– Pure components – Multicomponent mixture

– Dual fuel libraries

Group Chemistry Reference fuel for

Oxygenated methanol, ethanol, propanol Gasoline, Bio fuels

Mono aromats

toluene, m-xylene Gasoline, Diesel, Jet

Larger aromats

a-methylnaphtalene Diesel, Jet

Linear alkanes n-heptane, n-decane Gasoline, Diesel, Jet

Branched alkanes

iso-butane, iso-butene, iso-pentane, iso-octane, iso-dodecane

Gasoline, Diesel, Jet

Ester methyldecanoate Biodiesel

Additives DME Gasoline

Other methane, ethane, propane, butane, pentane, neo-Pentane, ethylene, acetylene, propene, hydrogen and others

Natural gas, Biomass to gas / liquid, turbines

Emission NOx, soot, formaldehyde, unburnt HC and other

Combinable with all fuels

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DARS v2.08 – Try it today!

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