A COMPREHENSIVE SOLUTION FOR EFFICIENT COMBUSTION SIMULATION WITH - - PowerPoint PPT Presentation

DARS FUELS – A COMPREHENSIVE SOLUTION FOR EFFICIENT COMBUSTION SIMULATION WITH DETAILED CHEMISTRY

FABIAN MAUSS

Demands on kinetic models

2

• 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

3

• 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

4

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.

5

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

6

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

7

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

8

*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

9

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

10

Laminar flame speeds at atmospheric pressure and different temperatures.

Example for a complete validation

11

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

Example for a complete validation

12

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

13

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

14

Species concentration over the hight of the burner in a (disturbed) burner stabilized flame at 1 atm.

Available mechanisms

15

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-

• ctane, 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

• ther

Combinable with all fuels

Multi-component Fuels example

16

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

17

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

18

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

19

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

20 *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

21

• 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