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DARS
FUEL MODEL DEVELOPMENT
2
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
6
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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