Reactive flows and complex

chemistry in DARS

Karin Fröjd

Enabling detailed chemistry in your CAE simulations

• Take the right design choices, including chemical effects

• Faster and cheaper design cycles

• Evaluation of entirely new designs

Why DARS?

What is DARS BasicTM?

Chemistry analyses

Mechanism reduction

Idealized reactors

– Ignition delay time

– Emission production

– Flame speed calculations

Library generation

1D & 0D PDF models for

in-cylinder combustion

and aftertreatment

Standalone software for 0D and 1D analyses of chemical reactions

DARS Basic v2.10 released!

- Focus on library generation for STAR-CCM+ and STAR-CD

Import any mechanism in DARS Basic

Analyse the chemistry in reactors and flames

Understand reaction pathways through species flow analysis

Chemistry analysis

Ignition delay times as function of

temperature for n-heptane

n-heptane decompositionCO production in fuel rich combustion of n-heptane

To avoid large CPU times the

mechanism can be reduced

Mechanism reduction through

necessity analysis

Visual analysis of the reaction

scheme through flow analysis

Steady state reduction through life-

time analysis

Mechanism reduction

Flow analysis for n-heptane

decomposition

Mechanism Reduction through necessity

analysis

Flow + sensitivity analysis used

to detect the most unnecessary

species in the mechanism

Workflow:

– Read detailed reaction scheme

– Run relevant reactor conditions,

with necessity analysis turned

on.

– Let DARS remove species with

necessity lower than your

defined threshold value

– Check mechanism validity

through rerun of relevant reactor

conditions

6Mechanism reduction panel – choose reduction limit here

DARS workbench – read mechanism, constant

pressure and reduce mechanism modules

DARS standard chemistry mechanisms

– n-heptane

– TRF (n-heptane/toluene)

– PRF (n-heptane/iso-octane)

– Natural gas

Collaboration with prof. Lu, Univ. of Connecticut

– n-dodecane

– PRF (n-heptane/iso-octane)

– Biodiesel

– DME

– Ethanol

– Natural gas

Any CHEMKINTM formatted mechanism from literature can be used

Chemistry mechanisms

Flow analysis for n-heptane

decomposition

1D channel model in DARS Basic

– Thin film layer approach - transport to washcoat calculated

– Surface chemistry in washcoat layer

– Gas phase chemistry in gas

– Detailed or global chemistry can be used.

– Any CHEMKIN format chemistry can be used.

DARS Basic - catalyst

washcoat

Monolith wall

DARS Basic - catalyst

DARS Basic - catalyst

Save time by analysing chemical

reactions in 1D before

employing full CFD

– Is detailed chemistry needed for

the CFD calculation?

– Can a reduced scheme be used?

– Optimization of chemistry

parameters for reduced schemes.

Study emission conversion as

function of

– Catalyst length

– Exhaust gas temperature

– Exhaust species composition10

0

200

400

600

800

1,000

1,200

-30 20 70 120 170 220

Tem

per

atu

re [

K]

/ C

on

cen

trat

ion

(p

pm

)

Time [min]

InletT[K]

NO_GasOut

NO2_GasOut

N2O_GasOut

NH3_GasOut

Ammonia SCR for a temperature ramp

C3H6 inhibition of NO oxidation

under lean conditions in Nox-

storage catalyst

With DARS Basic v2.10 you can export

– FGM libraries

– Soot libraries

– ECFM-3Z single/dual fuel libraries

– ECFM-CleH single/dual fuel libraries

– PVM-MF single/dual fuel libraries

Straightforward parameter specification,

designed for each library type

– Set up a full library calculation in less than 10

minutes.

Paralellization for efficient library

generation

Library generation

FGM libraries

Simulate combustion accurately

and fast

– DARS Basic can now export FGM

libraries for STAR-CCM+

– For non-premixed and partially

premixed combustion

Explore combustion of any

fuel/oxidant mixture

– Any CHEMKIN™ format chemistry

can be used

Improve species prediction

– Choose species for postprocessing

in STAR-CCM+.

Ignition process for n-heptane combustion at

various equivalence ratios

CO mass fraction during n-heptane combustion at

various equivalence ratios

Soot source term libraries

DARS Basic v2.10 can export Soot sectional and moment method libraries– Flamelets are used to capture

turbulence-chemistry interaction

Specify ranges and grid in T, P, EGR and scalar dissipation rate

Library set up ~ 10 min

Library calculation: ~ 40 h on 16 cores for single fuel library

13

The gas composition panel, used for specification of

parameter range and grid

Soot surface growth as function of mixture fraction for n-heptane

combustion at various strain rates

Thank you for your attention

www.cd-adapco.com/dars