HOW TO USE CHEMKIN

11 Example Gas-phase reaction mechanism (Gas-phase Kinetics Pre-processor input) ELEMENTS H O N END SPECIES H2 H O2 O OH HO2 H2O2 H2O N N2 NO END...

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HOW TO USE CHEMKIN 경원테크

Agenda ● CHEMKIN-PRO vs. Old Chemkin II ● CHEMKIN-PRO Overview ● Advanced Feature: Particle Tracking ● Advanced Feature: Reaction Path Analysis ● Example : Turbulent jet with kinetics & mixing ● Example : Catalytic oxidation ● Example : Gas-turbine combustor modeled by Reactor Network ● Example : Multi-Zone Engine Model for piston engines 2

Who is Reaction Design? • Software tool provider to the automotive, energy, and electronics markets since 1997

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CHEMKIN-PRO vs. Old Chemkin II FEATURE

Chemkin II

CHEMKIN-PRO

Combustion Reactor





Surface Chemistry



√ √

Automated Parameter Study

Solver Speed

Enhanced

Reaction Path Analyzer



Particle Tracking



Multi-Zone Engine Model



Enhanced Reactor Networking



Extinction Strain Rate



Command Line Operation

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Basic





Graphical User Interface



Tutorials



Technical Support



CHEMKIN-PRO is Much Faster

Simulation Speed-Up of CHEMKIN-PRO vs. CHEMKIN 5

Agenda ● CHEMKIN-PRO vs. Old Chemkin II ● CHEMKIN-PRO Overview ● Advanced Feature: Particle Tracking ● Advanced Feature: Reaction Path Analysis ● Example : Turbulent jet with kinetics & mixing ● Example : Catalytic oxidation ● Example : Gas-turbine combustor modeled by Reactor Network ● Example : Multi-Zone Engine Model for piston engines 6

Using CHEMKIN requires a chemistry set, reactor definition, and operating conditions Surface Chemistry

Gas Chemistry

ELEMENTS CHON END SPECIES CH4 O2 H2O N2 CO2 H2 O H OH CO … END REACTIONS H + H + M = H2 + M O + H2 = OH + H H + O2 = OH + O H + OH + M = H2O + M H2 + OH = H2O + H CO + O + M = CO2 + M …

Geometry and Flow Conditions

Hydrogen

Methane

Oxygen

Carbon Monoxide

Carbon Dioxide

Water

Hydroxyl

Transport Heat Transfer

Diffusive and Convective Transport 7

Running CHEMKIN requires definition of a Chemistry Set, which consists of several files ● Thermodynamic database – Must contain information for all species

● Transport database – Must contain information for all gas-phase species – Not required for many Reactor Models

● Gas chemistry reaction mechanism – Identify elements and gas species in system – Gas-phase reaction descriptions

● Surface chemistry reaction mechanism – Define surface and bulk species – Surface reaction descriptions 8

CHEMKIN is highly modular Gas Phase Chemistry / Thermodynamic Data Surface / Bulk Phase Chemistry / Thermodynamic Data

GAS-PHASE

SURFACE

TRANSPORT

KINETICS Utilities

KINETICS Utilities

Utilities

Application Input

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Transport Properties Input

CHEMKIN Application

Post-processing

Pre-processing of the chemistry set involves one to three steps ● Pre-processors create Linking Files that transfer chemistry-specific information to the Reactor Reactor Type

Equilibrium 0-D Closed and PSRs Plug-flow PaSR Shock-tube Shear-layer Channel flow 1-D Flame Simulators CVD Reactors Mechanism Analyzer LPCVD Furnace LPCVD Thermal

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Command-line Equivalents of Pre-processor commands

Transport Properties Database

Gas-phase Kinetics

Thermodynamic Database

Surface Kinetics

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chem –i chem.inp –d therm.dat -o chem.out surf -i surf.inp –d therm.dat -o surf.out tran –i tran.inp –d tran.dat –o tran.out

Example Gas-phase reaction mechanism (Gas-phase Kinetics Pre-processor input) ELEMENTS H O N END SPECIES H2 H O2 O OH HO2 H2O2 H2O N N2 NO END REACTIONS H2+O2=2OH 0.170E+14 0.00 OH+H2=H2O+H 0.117E+10 1.30 O+OH=O2+H 0.400E+15 -0.50 O+H2=OH+H 0.506E+05 2.67 H+O2+M=HO2+M 0.361E+18 -0.72 H2O/18.6/ H2/2.86/ N2/1.26/ OH+HO2=H2O+O2 0.750E+13 0.00 H+HO2=2OH 0.140E+15 0.00 O+HO2=O2+OH 0.140E+14 0.00 2OH=O+H2O 0.600E+09 1.30 H+H+M=H2+M 0.100E+19 -1.00 H2O/0.0/ H2/0.0/ H+H+H2=H2+H2 0.920E+17 -0.60 H+H+H2O=H2+H2O 0.600E+20 -1.25 H+OH+M=H2O+M 0.160E+23 -2.00 H2O/5/ H+O+M=OH+M 0.620E+17 -0.60 H2O/5/ O+O+M=O2+M 0.189E+14 0.00 H+HO2=H2+O2 0.125E+14 0.00 HO2+HO2=H2O2+O2 0.200E+13 0.00 H2O2+M=OH+OH+M 0.130E+18 0.00 H2O2+H=HO2+H2 0.160E+13 0.00 H2O2+OH=H2O+HO2 0.100E+14 0.00 O+N2=NO+N 0.140E+15 0.00 N+O2=NO+O 0.640E+10 1.00 OH+N=NO+H 0.400E+14 0.00 END

Reactions 11

47780 3626 0 6290 0

! ! ! !

D-L&W JAM 1986 KLEMM,ET AL DIXON-LEWIS

0 1073 1073 0 0

! ! ! ! !

D-L D-L D-L COHEN-WEST. D-L

0 0 0 ! D-L 0 ! D-L -1788 ! NBS 0 ! D-L 0 45500 3800 1800 75800 6280 0

Rate Coefficients: A, B, E

Species names must be consistent with thermo data

• • • •

H2/air Flame 3 elements 11 species 23 reactions

Thermodynamic data is required for both gasphase and surface chemistry ● Data are coefficients of polynomial fits to temperature for species specific heats, enthalpy, and entropy

c 0p

 a1  a2T  a3T 2  a4T 3  a5T 4

R a3 2 a4 3 a5 4 a6 H0 a2  a1  T  T  T  T  RT 2 3 4 5 T a3 2 a4 3 a5 4 S0  a1 ln T  a2T  T  T  T  a7 R 2 3 4 ● Data is fixed format to match historical NASA equilibrium code – Recent extensions allow more flexibility

● Thermo data also includes elemental composition of species

● Users may optionally include species thermodynamic data 12 in the reaction-mechanism input files

Example of thermodynamic data input Symbolic species name Species composition Temperature limits for fit ! “Break” temp. for 2-part fit ! Species: AL2H6 CAS Number: 12004-30-7 ! Name: Aluminum Trihydride, Dimeric ! Source: SNL fit to data generated from Pollard fit, 6/29/87 ! Comment: R. Pollard, J. Crystal Grow., V.77, P.200 (1986) ! H0(298K) = 21.3500 (Kcal/mole), S0(298K) = 62.7500 (cal/mole-K) AL2H6 62987AL 2H 6 G 300.000 1500.000 600.00 2.63488400e+00 2.13595200e-02 3.15415100e-07-7.68467400e-09 2.33583200e-12 8.87134600e+03 9.82751500e+00-6.80068100e+00 5.08074400e-02 1.03974700e-05 -1.11958200e-07 8.45915500e-11 1.06053700e+04 5.55452600e+01 ! ! Species: AL2ME6 CAS Number: 15632-54-9 ! Name: Trimethylaluminum, Dimeric ! Source: SNL fit to data generated from Pollard fit, 6/29/87 ! Comment: R. Pollard, J. Crystal Grow., V.77, P.200 (1986) ! H0(298K) = -61.2000 (Kcal/mole), S0(298K) = 131.050 (cal/mole-K) AL2ME6 62987AL 2C 6H 18 G 300.000 1500.000 600.00 1.77314700e+01 4.93574700e-02 1.19685400e-06-1.63982600e-08 4.89086700e-12 -3.85556000e+04-5.05329800e+01-7.15975000e-01 1.06710900e-01 2.11760500e-05 -2.19321200e-07 1.64414400e-10-3.51554600e+04 3.89076300e+01

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Comments provide more information about species

1 2 3 4

Data for one species

1 2 3 4

a1 – a7 for 1st fit range (high T)

Example of thermodynamic data input AL2H6 Thermodynamic Data

H0

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Cp0

S0

Example entries in transport data file Species Name AR AR* C C2 C2O CN2 C2H C2H2 C2H2OH CH2OH

Linearity 0 0 0 1 1 1 1 1 2 2

e/k 136.500 136.500 71.400 97.530 232.400 232.400 209.000 209.000 224.700 417.000

s 3.330 3.330 3.298 3.621 3.828 3.828 4.100 4.100 4.162 3.690

m 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1.700

a 0.000 0.000 0.000 1.760 0.000 0.000 0.000 0.000 0.000 0.000

Zrot 0.000 0.000 0.000 4.000 1.000 1.000 2.500 2.500 1.000 2.000

Lennard-Jones polarizability Lennard-Jones diameter rotational dipole well depth relaxation # moment 15

Example Surface Reaction Mechanism SITE/SILICON/ SDEN/1.66E-9/ Thermodynamic data for surface species SI(S) END is usually included in Surface Kinetics BULK SI(B)/2.33/ input file (rather than “therm.dat”) END THERMO ALL 300. 600. 1685. SI(S) J 3/67SI 100 000 000 0S 300.000 1685.000 1 0.24753989E 01 0.88112187E-03-0.20939481E-06 0.42757187E-11 0.16006564E-13 2 -0.81255620E 03-0.12188747E 02 0.84197538E 00 0.83710416E-02-0.13077030E-04 3 0.97593603E-08-0.27279380E-11-0.52486288E 03-0.45272678E 01 4 SI(B) J 3/67SI 100 000 000 0S 300.000 1685.000 1 0.24753989E 01 0.88112187E-03-0.20939481E-06 0.42757187E-11 0.16006564E-13 2 -0.81255620E 03-0.12188747E 02 0.84197538E 00 0.83710416E-02-0.13077030E-04 3 0.97593603E-08-0.27279380E-11-0.52486288E 03-0.45272678E 01 4 END REACTIONS SIH4 + SI(S) => SI(S) + SI(B) + 2H2 1.05E17 0.5 40000 SI2H6 + SI(S) => 2SI(S) + 2SI(B) + 3H2 4.55E26 0.5 40000 SIH2 + SI(S) => SI(S) + SI(B) + H2 3.9933E11 0.5 0.0 SI2H2 + 2SI(S) => 2SI(S) + 2SI(B) + H2 1.7299E20 0.5 0.0 2SI2H3 + 4SI(S) => 4SI(S) + 4SI(B) + 3H2 6.2219E37 0.5 0.0 H2SISIH2 + 2SI(S) => 2SI(S) + 2SI(B) + 2H2 1.7007E20 0.5 0.0 2SI2H5 + 4SI(S) => 4SI(S) + 4SI(B) + 5H2 6.1186E37 0.5 0.0 2SIH3 + 2SI(S) => 2SI(S) + 2SI(B) + 3H2 2.3659E20 0.5 0.0 2SIH + 2SI(S) => 2SI(S) + 2SI(B) + H2 2.4465E20 0.5 0.0 SI + SI(S) => SI(S) + SI(B) 4.1341E11 0.5 0.0 H3SISIH + 2SI(S) => 2SI(S) + 2SI(B) + 2H2 1.7007E20 0.5 0.0 SI2 + 2SI(S) => 2SI(S) + 2SI(B) 1.7607e20 0.5 0.0 SI3 + 3SI(S) => 3SI(S) + 3SI(B) 8.6586E28 0.5 0.0 END 16

CHEMKIN: A set of tools designed to model complex chemical kinetic processes ● CHEMKIN Reactor Models represent idealized conditions – Example: Cylindrical Shear-flow Reactor

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Reactor models represent different geometries and flow conditions

Plug-flow Reactor (PFR) Perfectly Stirred Reactor (PSR) (CSTR)

Partially Stirred Reactor

T v

Pre-mixed Flame

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Opposed-flow Diffusion Flame

T v

Shear-layer Channel-flow Reactor Flame-speed Calculation

CHEMKIN-Pro Reactor Model 0-D reactor Closed Homogeneous Batch Reactor

Plug Flow Reactor(PFR)

Closed Partially Stirred Reactor

Plasma plug Flow Reactor

Closed Plasma Reactor

Cylindrical Shear Flow Reactor

Single zone HCCI Engine

Planar Shear Flow Reactor

Multi zone HCCI Engine

Honeycomb Monolith reactor

Perfectly Stirred Reactor(PSR) Partially Stirred Reactor(PaSR) Plasma PSR 19

1-D reactor

CHEMKIN-Pro Reactor Model Flame Simulation

Shock Tube Reactors

Premixed Laminar Burner-stabilized Flame

Normal Incident Shock

Premixed Laminar Burner-stabilized Stagnation Flame

Normal Reflected Shock

Premixed Laminar Flame-speed Calculation

CVD Reactor

Premixed Laminar Flame-speed Library

Stagnation Flow CVD Reactor

Diffusion or Premixed Opposed-Flow Flame

Rotating Disk CVD Reactor

Extinction of Diffusion or Premixed Opposed-Flow Flame

LPCVD Reactor LPCVD Thermal Analyzer LPCVD Furnace

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Closed Reactors include homogeneous and mixing models ● Internal Combustion Engine cylinder model – Volume vs. time sweep – Homogeneous mixture – Compression ignition

R

Yk

P I

● Generic “Batch Reactor” model – Heat-transfer options – Constrained volume or pressure – Allows gas and surface chemistry

time

● Closed Plasma model

● Closed Partially Stirred Reactor 21

– Constrained volume or pressure – Track mixing and kinetics time-scales

Sensitivity

– Electron energy equation – Specified power-deposition – Allows gas and surface chemistry

Reaction #4 Reaction #2

Reaction #18

time

Open 0-D reactors provide basic flow elements and 1st-order approximations ● Generic Perfectly Stirred Reactor (PSR) – Allows gas and surface chemistry – Steady-state or transient mode – Can be clustered

● Perfect Mixer – No chemistry – Steady-state or transient mode – Can be clustered

● Open Plasma Reactor – – – – –

Allows gas and surface chemistry Electron energy and plasma power deposition Ion impact energy for surface chemistry Steady-state or transient mode Can be clustered

● Partially Stirred Reactor (PaSR) 22

– Turbulent-kinetics interactions

Clusters of open 0-D reactors allow mass and heat “recycling” to simulate complex flows ● Multiple inlet streams – Different composition, Temperature, flow rate

● Recycle streams between reactors – User-specified recycle fractions & paths

● Heat transfer between reactors – Convection / conduction and/or radiation

● Perfectly stirred reactor elements R31

Inlet A

Inlet B

Inlet C

1

R13

2

3 R32

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R11

Outlet

Flows where axial convection dominates can be modeled as plug-flow ● Generic Plug-flow Reactor – Reactor is assumed uniform in cross-flow direction – Neglect diffusion – Independent control of heat-loss and surface-chemistry areas

R

Yk

P I

Distance

● Honeycomb Monolith Reactor – Active surface area and hydraulic diameter determined from geometry

● Plasma Plug-flow Reactor – Electron energy equation – Power deposition over length of channel

Approximate as Surface Area per unit of distance

All include sensitivity analysis, heat-transfer options, and both gas-phase and surface chemistry 24

Open 0-D and plug-flow reactor models have unique surface-chemistry capabilities ● Treatment of Multiple Materials – Use MATERIAL keyword in Surface Kinetics input file – Specify separate chemistry on different materials – Control relative surface areas of materials

● Modeling of Plasma/Surface Interactions – Ion/electron recombination – Ion-enhanced etching and etch yields

● Sensitivity analysis for Gas & Surface Chemistry – Transient and steady-state

● Rate-of-production analysis – Transient and steady-state – Gas and surface reactions 25

Shear-layer Flow Reactors account for boundary-layer interactions ● Cylindrical Shear-flow Reactor – Boundary-layer approximation of flow field in cylindrical coordinates – Provides spatial variation in radial or transverse direction – Includes radial diffusion – Neglects axial diffusion o

Axial convection dominates

– Variety of heat-transfer options – Gas and surface chemistry

● Planar Shear-flow Reactor – Boundary-layer approximation in planar coordinates

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1-D Flame Models provide detailed flamestructure and balance transport and kinetics ● Pre-mixed Burner Model – – – –

Pre-mixed fuel and oxidizer Burner-stabilized flame Laminar flow Heat-of-formation and Reaction-rate sensitivity analysi

● Pre-mixed Flame-speed Calculator – – – – –

Predict adiabatic flame-speed Determine flammability limits and flame thickness Effects of heat loss and radiation transfer Laminar flow Heat-of-formation and Reaction-rate sensitivity analysi

● Opposed-flow Diffusion Flames

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– Similarity transformation converts 2-D planar or 3-D axisymmetric into 1-D model – 1-D boundary conditions assumed – Diffusion-flame flammability limits – Flamelet model for generating CFD look-up tables – Heat-of-formation and Reaction-rate sensitivity analysis

CHEMKIN’s normal-shock models can be used to simulate shock-tube experiments ● Incident Shock Model – Users specify conditions before the shock wave – Gas-dynamic relations determine initial post-shock conditions – Transient kinetics after shock has passed – Viscosity effects can be included

● Reflected Shock Model – Gas-dynamic relations determine conditions after reflected shock – Transient kinetics start after reflected shock passes Incident Shock U2

2

Reflected Shock

1

Us

U2

2

Urs

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Agenda ● CHEMKIN-PRO vs. Old Chemkin II ● CHEMKIN-PRO Overview ● Advanced Feature: Particle Tracking ● Advanced Feature: Reaction Path Analysis ● Example : Turbulent jet with kinetics & mixing ● Example : Catalytic oxidation ● Example : Gas-turbine combustor modeled by Reactor Network ● Example : Multi-Zone Engine Model for piston engines 29

Particle Tracking in CHEMKIN-PRO Get fast and accurate answer to “ what if …” questions -

Predict particle properties, mass emission and size distribution Wide range of reactor models to fit your application

Use accurate gas-phase and surface chemistry -

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Nucleation Agglomeration Surface growth

Two options depending on the answer you need … -

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Method of Moments model :  Average size, total mass emissions Sectional model:  Adds information on particle size distribution

Example: Soot in a Jet-Stirred Reactor(JSR) JSR/PFR system developed at MIT (Marr, 1993) Chemistry: -

-

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Gas-phase: Ethylene/Air (includes formation of PAH precursors) Surface mechanism includes nucleation, oxidation and pyrene and PAH condensation reactions Use Method of Moments for average diameter and number density

Example: Soot in a Jet-Stirred Reactor(JSR) 1630K, Φ=2.2 Case of the C2H2/O2/N2

Soot Mass Concentration 32

Particle Diameter Evolution

Example: Premixed Stagnation Flame Premixed ethylene/air flame impinging on a wall -

Gas-phase: Ethylene/Air (includes formation of PAH precursors)

Sectional method for size distribution information -

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Size coordinate (D) is divided into sectional bins

Agenda ● CHEMKIN-PRO vs. Old Chemkin II ● CHEMKIN-PRO Overview ● Advanced Feature: Particle Tracking ● Advanced Feature: Reaction Path Analysis ● Example : Turbulent jet with kinetics & mixing ● Example : Catalytic oxidation ● Example : Gas-turbine combustor modeled by Reactor Network ● Example : Multi-Zone Engine Model for piston engines 34

Reaction Path Analysis in CHEMKIN-PRO Identification of dominant pathways

Determination of pathways contributing to pollutant formation Determination of changes in pathways due to variation of operating conditions Guiding of mechanism reduction efforts

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Reaction Path Analysis in CHEMKIN-PRO Reaction path diagram

Control of reaction path

start : CH4

start

Species sensitivity Color : species (red : OH)

Species : rate of production

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End

The number of species Dynamic selection of location in solution

Reaction Path Analysis in CHEMKIN-PRO

Rate of production for a path

Rate of progress 37

Agenda ● CHEMKIN-PRO vs. Old Chemkin II ● CHEMKIN-PRO Overview ● Advanced Feature: Particle Tracking ● Advanced Feature: Reaction Path Analysis ● Example : Turbulent jet with kinetics & mixing ● Example : Catalytic oxidation ● Example : Gas-turbine combustor modeled by Reactor Network ● Example : Multi-Zone Engine Model for piston engines 38

In many real systems, e.g. turbulent jets, perfect mixing cannot be assumed Gas turbines* – Mixing zone with pre-mixed fuel and re-circulated burned products » ignition time delay

– Flame zone – Post-flame zone with cool air addition

Industrial burners – Jet entrance region

Internal combustion engines – Effect of residual gas trapped on ignition time delay

*Ref: 39

S.M. Correa, Combustion and Flame 93:41-60 (1993). J.-Y. Chen, Combustion Science and Technology 122:63-94 (1997)

The Partially Stirred Reactor (PaSR) addresses turbulence-kinetics interactions Considers effects of mixing on the kinetics of a combusting system – Uses Monte Carlo mixing method – Allows detailed kinetics

Explores effects of mixing time scale, relative to the reactor residence time,

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 mix  res

PaSR is a computationally efficient means for considering chemistry and mixing Sequential Monte Carlo Simulation of Probability Density Functions for Species*: ~ ~ P t  t   I  tC  tM  tK P t   Ot  Chemical Reaction Molecular Mixing Convection Identity Operator

t 41 *Ref: S.B. Pope, Combustion Science and Technology 25:159-174 (1981)

The partially stirred reactor model tracks turbulent mixing and reaction in a zone Consider two reacting streams: Inlet 1 = 100% A

Inlet 2 = 100% B

Reaction A+BC

Mixing and Reaction Zone

Time t = 0 42

PaSR considers convection, molecular mixing, and kinetics in each time step

Convection

Molecular Mixing

Kinetics options: – No reactions – Equilibrium calculation – Full finite-rate CHEMKIN kinetics

Chemical Reaction

Reaction A+ BC

Molecular Mixing options : – Modified Curl’s Model – Interaction by Exchange with Mean (S. Correa) 43

Time t = t

Input required to define a PaSR Residence time of the mixing zone (based on flow rate)

Characteristic Mixing time – –

 mix  k e

Estimate based on flow (e.g. CFD calculation) Range ~ ms to s

Chemical reaction mechanism – –

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Gas-phase Kinetics Input file Thermodynamic data

The PaSR input, Mixing Timescale, is a characteristic of the turbulent flow field May be determined from a CFD calculation – CFD flow simulation provides k, epsilon –  mix  k e

Small values make a PaSR behave like a perfectly stirred reactor (PSR)

 mix   res

Large values make a PaSR behave like a plug flow reactor (PFR)

 mix   res

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Comparison of two mixing models Modified Curl’s Model

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Interaction by Exchange w/ Mean

Example: Turbulent mixing and kinetics for H2 fuel and air Consider a jet of H2 into hot air How does mixing affect ignition?

Air H2

time

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Air

Air Reaction and mixing

Reaction and mixing

Example: Turbulent mixing and kinetics for H2 fuel and air Model options

Jet conditions – General o o

– Include chemistry – Use Curl’s mixing model

Pressure = 1 atm Simulation time = 5 msec

» Factor = 1

– Air Entrainment o o

– Solution method

Flow rate = 1 g/s Temperature = 1500 K

» Backwards differencing

– Monte Carlo options

– Initial conditions of jet o o

» Number of particles (number of statistical events) = 400 » Time step = 1.E-5 sec

Pure H2 fuel Temperature = 300 K

– Characteristic times o o

Residence = 1.E-3 sec Mixing = 1.E-4, 1.E-5, or 1.E-6 sec

H2

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Air

Air

Air

Reaction and mixing

Reaction and mixing

Example: Turbulent mixing and kinetics for H2 fuel and air Results show effects of mixing on ignition Temperature

Mean values OH

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Example: Turbulent mixing and kinetics for H2 fuel and air PaSR saves a probability distribution function (pdf) at the end of the run for a specified variable – “pdf.plt” file

The file can be imported into the Graphical Postprocessor and plotted

MIXT / TAU = 0.001

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Agenda ● CHEMKIN-PRO vs. Old Chemkin II ● CHEMKIN-PRO Overview ● Advanced Feature: Particle Tracking ● Advanced Feature: Reaction Path Analysis ● Example : Turbulent jet with kinetics & mixing ● Example : Catalytic oxidation ● Example : Gas-turbine combustor modeled by Reactor Network ● Example : Multi-Zone Engine Model for piston engines 51

Characteristics of Catalytic Oxidation Compared to homogeneous combustion: 1. Flameless process even though heat is released 

Less sooting

2. Generally proceeds at lower temperatures 3. Lower emissions of NOx are typical 4. Combustion occurs over a wider range of fuel/air ratios (c.f. CH4 5-15%) 

Stability / robustness of process

5. Facilitates flexibility in burner designs 52

Example: Catalytic Oxidation in Turbines The Challenge: Improve efficiency and reduce pollutant emissions (NOx) Main Fuel Pre-burn Fuel

Catalyst Monolith

Exhaust

Compressor Stage Main features of GE and Allison Systems Designs 53

Turbine Stage

Simulation requires detailed surface chemistry and flow model of monolith Surface Chemistry Oxygen

Methane

Carbon Monoxide

Hydroxyl

Reaction Mechanism

Hydrogen

Carbon Dioxide

Water

Geometry and Fluid Flow

Surface Reactions

Gas Phase Reactions

Heat Transfer

Diffusive and Convective Transport 54 Ref: L. L. Raja, R. J. Kee, O. Deutschmann, J. Warnatz, L. D. Schmidt, Catalysis Today, 59 (2000) 47-60

Example:

Catalytic oxidation of CH4 on Pt with Shear-layer Flow

● Shear-layer flow includes surface kinetics and boundarylayer effects (PFR won’t do)

● Example: – Pre-burn catalytic oxidation component in gas turbine – CH4 oxidation on Pt – Neglect gas-phase chemistry

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Example: Monolith Tube

Catalytic oxidation of CH4 on Pt with Shear-layer Flow Adiabatic Q=0

Pt Catalyst

1 mm

3% CH4 in air u = 5 m/s T = 770 K P = 1 atm.

20 cm Model a single channel in the monolith

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Surface mechanism includes – 8 gas-phase species – 11 surface site species – 22 surface reactions

Example:

Catalytic oxidation of CH4 on Pt with Shear-layer Flow

● Is there a “flame”? ● How far down the channel does “light-off” occur? ● What is the optimal channel length for converting CH4 to CO2 – On what parameters will this depend?

● What would you expect the effect of adding gas chemistry to be? – Would NOx production be high?

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Example:

Catalytic oxidation of CH4 on Pt with Shear-layer Flow

● Results show a lot happening at around 1112 cm along the channel

Simulation is axisymmetric 58

Example:

Catalytic oxidation of CH4 on Pt with Shear-layer Flow

Conversion appears to be complete!

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Example:

Catalytic oxidation of CH4 on Pt with Shear-layer Flow

● Velocity profiles fully developed at ~ 4 cm

Velocity Profiles at beginning of Channel Distance Along Channel

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Example:

Catalytic oxidation of CH4 on Pt with Shear-layer Flow

● The surface self-heats due to the surface oxidation kinetics ● At ~ 10 cm, the reaction takes off, T goes to 1485 K ● No flame – the wall is always the hottest point

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Example:

Catalytic oxidation of CH4 on Pt with Shear-layer Flow

● The gas equilibrates quickly with the wall due to the thinness of the channel

Aspect ratio is 200:1

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Centerline

Wall

Example:

Catalytic oxidation of CH4 on Pt with Shear-layer Flow

Surface profiles show light-off behavior Surface site coverage critical to catalyst behavior

Exothermal Reaction Kicks In

63

Agenda ● CHEMKIN-PRO vs. Old Chemkin II ● CHEMKIN-PRO Overview ● Advanced Feature: Particle Tracking ● Advanced Feature: Reaction Path Analysis ● Example : Turbulent jet with kinetics & mixing ● Example : Catalytic oxidation ● Example : Gas-turbine combustor modeled by Reactor Network ● Example : Multi-Zone Engine Model for piston engines 64

A gas turbine combustor may be modeled as a PSR network with a PFR at the end. Air

Air Premixed Fuel + Air Fuel + Air Air

Mixing Zone

Recirc. Zone

Flame Zone Air perfectly-stirred reactors 65

Post-Flame Zone plug-flow reactor

Example: Gas-turbine combustor with reactor network Results from 3 PSR Network 2 4

1

3

O2

CH4 66

H 2O

CO2

Using PFR for post-flame provides more accurate prediction of emissions

Temperature

NO Fraction

Radical Species

OH CO

O H

67

PFR Results

Accurate Reactor Networks are Complex

68

Agenda ● CHEMKIN-PRO vs. Old Chemkin II ● CHEMKIN-PRO Overview ● Advanced Feature: Particle Tracking ● Advanced Feature: Reaction Path Analysis ● Example : Turbulent jet with kinetics & mixing ● Example : Catalytic oxidation ● Example : Gas-turbine combustor modeled by Reactor Network ● Example : Multi-Zone Engine Model for piston engines 69

Multi-zone Engine Model Zone Definition

70

Multi-zone Engine Model Results

71