DARS FUELS –

A COMPREHENSIVE SOLUTION FOR EFFICIENT COMBUSTION SIMULATION WITH DETAILED

CHEMISTRY

FABIAN MAUSS

Demands on kinetic models

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• Combination of different fuel components …for most realistic surrogate fuels

• Comprehensive mechanisms …to cover a wide range of conditions

• Reliable models …a user can not test each model

• Consistency …to ensure a predictive chemistry in all sub-models

• Fast calculation times …to work cost and time efficiently

• Table approaches …compatible with CFD software

The variable mechanism concept

• Free combination of models • The base chemistry - contains

fuels from C1 to C6 • Larger fuel molecules can be

combined with the base chemistry

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• Aliphatic Compound 1 • Aliphatic Compound 2 • Aliphatic Compound 3

• Alcohol 1 • Alcohol 2 • Alcohol 3

• Ester 1 • Ester 2 • Ester 3

Base Chemistry • Aromatic Fuel 1 • Aromatic Fuel 2 • Aromatic Fuel 3

NOx Soot PAH

• Mechanisms for emission formation

• All these mechanisms can be combined into a reaction-mechanism according to needs.

Validation Base chemistry I

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Experimental and simulated laminar flame speed for fuels, toluene, n-heptane, iso-octane, ethanol, methanol, methane, ethane, propene, ethylene, propane, butane, acetylene. Most experiments at 1bar and 300K. All data plotted with an offset for better presentation. Details can be found from Hoyermann et. al. 2004.

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Experimental and simulated ignition delay times for: methane, ethylene, ethane, propene, propane, n-butane, iso-octane, methanol, ethanol and hydrogen. Data plotted with an offset for better presentation. Details can be found from Hoyermann et. al. 2004.

Validation Base chemistry II

Validation targets

All mechanism are validated against available experiments in:

• Shock tube

• Flow reactor

• Rapid compression machine

• Flames: burner stabilized, freely propagating, counter flow

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Covering wide ranges:

• Pressure (200mbar – 70bar)

• Temperature (500K – 2000K)

• Mixture fraction (very lean to rich conditions and pyrolysis)

• Dilution

Against different targets :

• Ignition delay

• Fuel decomposition

• Intermediates

• Emission

• Heat release

• Flame speeds

Key Features

Reduced stiffness

• Using different techniques to reduced the stiffness of a mechanism -> short computational time, even with detailed models

Compact even in detailed format

• Only species which are important for the decomposition of the fuel are included

Multiple formats

• The mechanisms are available in various formats

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Libraries for CFD software

• Pre compiled libraries for direct use in simulations

• Compatibility with STAR-CD products

Consistency

• Reaction

• Names

• Thermodynamic data

• Transport properties

Key Features

Good documentation

Rule based Semi Automatic Generation*

• Mechanism generation for larger alkanes based on rules

• Rules tested against several alkanes

• Extrapolation to fuels without experimental base

• Automatic graph based generation -> efficient and less error prone

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*M. Hilbig, L. Seidel, X. Wang, F. Mauss, and T. Zeuch. ´“Computer aided detailed

mechanism generation for large hydrocarbons: n-decane.” 23rd ICDERS, 2011.

Soot

• Integrated modeling of soot precursors

Complete solution

• From mechanism development to table generation

• From detailed reaction schemes to highly reduced, special purpose mechanisms

Constant development

• Constant improvement and development of new models

Example for a complete validation

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Complete validation for an n-decane reaction mechanism. Validation against all available experiments in literature for:

• flames • perfect stirred reactor and • shock tubes

Specifications:

• Detailed: 374 species ⁻ including detailed NOx, soot formation and all fuels from the base

chemistry. • Skeletal: 193 species

- including detailed NOx, soot formation and a reduced set of fuels in the base chemistry

Example for a complete validation

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Laminar flame speeds at atmospheric pressure and different temperatures.

Example for a complete validation

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Concentration of major species in a Jet Stirred Reactor at 10 atm.

Example for a complete validation

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Ignition delay times in a shock tube

at Φ=0.25. Ignition delay times in a shock tube

at Φ=0.5 and Φ=0.67.

Example for a complete validation

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Ignition delay times in a shock tube

at Φ=1.0. Ignition delay times in a shock tube

at Φ=2.0.

Example for a complete validation

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Species concentration over the hight of the burner in a

(disturbed) burner stabilized flame at 1 atm.

Available mechanisms

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Group Chemistry Reference fuel for

Oxygenated methanol, ethanol, propanol Gasoline, Bio fuels

Mono aromats toluene, m-xylene Gasoline, Diesel, Jet

Larger aromats a-methylnaphalene Diesel, Jet

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

Branched alkanes iso-butane, iso-butane, 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

Multi-component Fuels example

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Ignition dealy times for a mixture of 56% iso-octane,

17% n-heptane and 28% toluene at 50bar.

Variation of Φ=0.5, 1.0, 2.0

Ignition dealy times for a mixture of 62% iso-octane,

18% n-heptane and 20% toluene at Φ=1.0.

Variation of pressure: 30bar, 50bar

Reference Fuels

Gasoline specifications in different countries

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Properties Euro 4* USA Japan**

ROZ (Regular) min. 95 min. 90 min. 89 typical around 92

ROZ (Premium) min. 98 min. 95

min. 96 typical around 100

Ethanol up to 10% in regular up to 3%

Aromat content (vol %)

max. 35 max. 22 (California) No regulation - typical around 22%

(Regular) to 37% (Premium)

Ethanol Fuels max. 10% in Regular E5 / E10 / E75 / E85

E10 / E85 / E95 -

* DIN EN 228

** JSAE Review 21 (2000) 457-462

Reference Fuels

• Combustion Behavior

– Ignition delay time

– Octane / Cetane Number

– Emission formation

• Direct testing in engine models

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Development of reference fuels based on different criteria:

• Physical Properties

– Density

– Lower Heating Value

• Chemical Properties

– Fraction of chemicals in the fuel, such as aromatics, alkanes, ester…

– Ignition behavior

– Boiling line

EURO 4 - E5 Reference Fuel

4 Component E5 reference fuel

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Properties Target Mixture

ROZ 95 95

LHV [MJ/kg] 40,1 – 41,8 41,0

Ethanol [vol %] 5 5

Aromatic [vol %] 35 35

Density [kg/L] 0,72 – 0,775 0,74

Reference fuel (mole fraction):

• ethanol: 0.11

• toluene: 0.405

• iso-octane: 0.354

• n-heptane: 0.131

Reduction / Tables

Reduction of reaction schemes size using:

– Horizontal lumping*

– Chemical guided reduction*

Various table solutions

– Can be used with STAR-CD, STAR-CCM+

– Precompiled from detailed reaction schemes, ready to use

– Covering a wide range of engine conditions

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*S. Ahmed, F. Mauss, and T. Zeuch.“The generation of a compact

n-heptane/toluene reaction mechanism using the chemistry

guided reduction (CGR) technique.” Z. Phys. Chem.,

223:551{563, 2009

– ECFM

– Flamelet Soot

• Soot source term library

– Flamelet NOx

• NOx source term library

– Flame Speed

• Laminar flame speed, used by e.g. Level-Set and ECFM models

– PVM

• Progress variable auto-ignition and thermodynamics library

DARS Fuel

• Accurate reaction schemes – ready to use!

– Plug in to STAR-CD, STAR-CCM+, DARS-TIF

– No additional work needed

• Free basic libraries for ECFM

– Diesel

– Gasoline

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• Free basic mechanism for TIF/PVM

– Diesel

– Gasoline

– Requires a DARS license

• Other fuels are available as library on license base

– Pure components

– Multicomponent mixture

– Dual fuel libraries

Thank you for your attention