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Chemical kinetic modeling development and validation experiments for direct fired sCO2
combustor PI: Subith Vasu1
Co-PIs: Jayanta Kapat1, Artem Masunov1, Scott Martin2, Ron Hanson3
1University of Central Florida, Orlando, FL2Embry-Riddle University, Daytona Beach, FL
3 Stanford University, Stanford, CA
DE-FE0025260PM: Dr. Seth Lawson
Duration 3 years: 10/1/2015-9/30/2018UTSR Meeting, Daytona Beach, FL, 11/1/2018
Distribution A: Approved for public release
Contact: subith@ucf.edu
Direct-fired sCO2 combustionIdeal Oxy-fuel combustionCH4 + O2 + CO2 → CO2 + H2O
CO2 is directly-fired based onthe Brayton Cycle ConceptTypically highest pressuresranges from 200 - 300 bar athigh pressures to just abovethe critical point
Figure adapted from Strakey, 2014, sCO2 symposium Figure adapted from Delimont, 2016, sCO2 symposium
• Existing state‐of‐the‐art, such as GRI‐3.0 Mechanism, has only been validated for pressures up to 10 atm
• Mechanisms have not been developed for CO2 diluted mixtures
• Updated/new mechanism will allow for accurate combustor modeling with multi‐step combustion using a validated mechanism
• Current CFD combustion models do not consider non‐ideal effects
• Thermodynamics and kinetics are currently unknown!!
• Fundamental work can shed light into this challenge
Knowledge gaps
Effects of Increasing Pressure. Equilibrium calculation for CH4/O2/CO2 at φ = 1. Figure adapted from Strakey, 2014, sCO2 symposium
State-of-the-knowledgeState‐of‐the‐art models differ in their predictions even at atmospheric pressure with high CO2
• GRI 3.0 is still a widely used mechanism created 15 years ago• Aramco Mech 2.0 is a recent well‐validated mechanism
Combustion chemistry snapshot
ReactionMechanismDevelopment
1. DecompositionPathways
2. IntermediateSpecies Sub‐Mechanisms
3. Full Mechanisms
4. Reduced Mechanisms
5. Validation
MODEL
KineticTargets(Shock Tubes, FlamesReactors)
1. Ignition Time Measurements
2. SpeciesTime‐Histories
3. Direct Rate Measurements
4. Flame speed
5. Ignition energy, pressure rise
EXPERIMENTSFuel +O2+CO2
InitialDecomposition
Products
Intermediate Species
H-Abstraction& Oxidation
Products
Ignition
CO, CO2, H2O
OH, CH3, C2H4, C2H2, H2, CO, etc.
time=0
time= µs
time= ms
time= s
Combustion chemistry/kinetics are different at high pressure1 bar 300 bar
(Strakey, SCO2 symposium 2018, NETL)
Project/Task Summary
Task 1: Project Management
Tasks 2&3: Acquire kinetics and ignition data in highly CO2 diluted mixtures with shock tube experiments
Task 4: Refine and validate a chemical kinetic mechanism for Supercritical Carbon Dioxide (sCO2) Mixtures
Task 5: Develop a CFD Code that utilizes mechanism for sCO2 combustors
Overall Progress from this project in 3 years Oxy-Combustion/SCO2
- 20 Journal Papers
- 3 in J. Engineering for Gas Turbines and Power (ASME)
- 4 in J. Energy Resources Technology (ASME)
- 2 in Combustion and Flame
- 7 in J. Physical Chemistry A
- 2 in Energy & Fuels
- 1 Int J Chemical Kinetics
- 1 Proc. of Combust. Inst.
- > 30 conference papers at ASME Turbo Expo, sCO2 symposium, AIAA Meetings, Combustion Institute Meetings
- 4 additional journal papers currently in review
Sample Experiments Results
Shock tube operation: Pre-shock filling
High P Low P
Driver section
(high-pressure)
Driven section
(low-pressure)
Optical diagnostics for
absorption,
emission
DiaphragmPressure
transducers
4 1
Shock tubes are ideal for studying combustion chemistry Step change in T, P and well-defined time zero Simple fuel loadingAccurate mixtures and pre-shock conditions
Laser absorption spectroscopy
Beer - Lambert law
Spectral absorption coefficientkλ= S(T)ꞏ(T,P,X)
S(T): line strength, (T,P,X): line shape
Io
IPhoto detector
Laser source
L
I/Io = exp (-k Ptotal Xspecies L)32600 32610 32620 32630 32640
0
20
40
60
80
k [a
tm-1
cm-1
] [cm-1]
= 306.47nm
Ignition Results: Without CO2• Comparison of measured and simulated methane concentration for– Stoichiometric ignition of 3.5% CH4 in Argon, 1600K
0 500 1000 1500 20000.00
0.05
0.10
0.15
X CH
4
Time [sec]
XCH4 (Measured) XCH4 (Aramco) XCH4 (GRI)
0.0
0.5
1.0
1.5
2.0
2.5 CH* Pressure
P [a
tm] /
CH
*With out CO2 addition there is pressure rise after ignition
• Ignition delay times measured from the arrival of reflected shockwave to rise of the pressure trace
• Arrival of shockwave determined as midpoint of the second pressure rise (rise due to reflected shock)
• Rise of OH Emissions measured asthe intersection between the baseline and the tangent line drawn from maximum rise of OH
Ignition Results: 60% CO2 addition• Comparison of measured and simulated methane concentration for– Stoichiometric ignition of 3.5% CH4 in Argon diluted with 30% CO2, 1600K
0 100 200 300 400 5000.00
0.05
0.10
0.15
X CH
4
Time [sec]
XCH4 (Measured) XCH4 (Aramco) XCH4 (GRI)
0.0
0.5
1.0
1.5
2.0 CH* Pressure
P [a
tm] /
CH
*
With CO2 addition there is no pressure rise after ignitionTrue observation for all mixtures?
Ignition Results in CH4 Under SCO2 Conditions: 77.5% CO2 addition
With CO2 addition there is some pressure rise (7.5% fuel) after ignition but not as bad as the ones without CO2
0 100 200 300 400 5000
5
10
15
20
Time (s)
Pres
sure
Sig
nal (
volts
)
7.5% CH4/ 15% O2 /CO2
1277 K, 111.8 atmign = 367 s
Non-reactive Pressure
Pressure
OH* Emission
0.0
0.1
0.2
0.3
0.4
0.5
OH
* Em
issi
on
Ignition Results in CH4/O2 Under SCO2Conditions: 85% CO2 addition
With CO2 addition there is no pressure rise after ignition (4% fuel)
0 500 10000
5
10
15
Time (s)
Pres
sure
Sig
nal (
volts
)
3.91% CH4/ 9.92% O2 /CO2
1352 K, 75.1 atmign = 541 s
Pressure
OH* Emission
0.00
0.01
0.02
OH
* Em
issi
on
Low CH4 Loading: 3.9% CH4/O2/CO2 data: =0.7885% CO2 addition
• Small scatter in IDT data
• ARAMCO and FFCM in excellent agreement with IDT up to 80 atm
• But two models differ significantly at high pressure (260 atm)
Next: How do the models compare with higher fuel loading?
0.7 0.8 0.9100
1000
100001429 1250 1111
Temperature (K)
Igni
tion
Del
ay T
ime
(ms)
1000/T (1/K)
Modeling:Solid: ARAMCO Ver. 2 (2013)Dash: FFCM (2018)
80 atm 260 atm
39 atm
0.7 0.8 0.9 1.010
100
1000
100001429 1250 1111 1000
Temperature (K)
Igni
tion
Del
ay T
ime
(s)
1000/T (1/K)
Modeling:Solid: ARAMCO Ver. 2 (2013)Dash: FFCM (2018)
110 atm
33 atm
High CH4 Loading 7.5% CH4/O2/CO2 data: =1.085% CO2 addition
• Good agreement of models with data at 33 atm
• Continue good agreement up to 110 atm
• But models diverge at low T
CO2-diluted Ignition Experiments are challenging: High-Speed Imaging for Accurate Ignition Determination
19
Reflected Shock Bifurcation• Bifurcation is a result of differences in the energy level between the
boundary layer and core flow. Occurs with diatomic and polyatomicmolecules in the driven section
• Bifurcation induces inhomogeneities 100μ
s15
0μs
200μ
s
Reflected shock Endwall
4 cm
Adapted from Kline et al. ISSW 1992Penyazkov et al., 2016 SW
Adapted from Yoo, Hanson, et al. 2010
Methane/O2/CO2 Ignition Imaging Results CO2=89.5%
Experiments with CO2 addition is not trivial in shock tubes Boundary layer effects, shock bifurcation
Solution Use multiple diagnostics to study ignition process
Methane/O2/CO2 Ignition: High-Speed Imaging Results CO2=0 %
--------------Ignition sequence imaged via high-speed (63, 000 fps)-------------
22
Methane/O2/CO2 Ignition Imaging ResultsCO2=85%
23
Methane/O2/CO2 Ignition Results With Imaging
(a) Mixture 1: XCH4 = 0.035, XO2 = 0.07, XCO2 = 0.00, XAr = 0.895. No CO2
(b) Mixture 2: XCH4 = 0.035, XO2 = 0.07, XCO2 = 0.60, XAr = 0.295. 60% CO2
Difference in various definitions increase with addition of CO2However, the data can be compared to modeling predictions for various definitions
Select Syngas/O2/CO2 Ignition Delay TimesNote: Syngas fuel is a mixture of CO and H2
-200 0 2000.0
0.2
0.4
0.6
0.8
1.0
1.2
T = 1203 KP = 120 atmTpeak= 76.5 usTslope= 62 us
Nor
mal
ized
Em
issi
on
Time [s]
Normalized OH* Emission Measured Pressure
Mixture:CO= 16.653%H2= 6.969%O2= 11.887%CO2=64.491%
0
20
40
60
80
100
120
140
160
180
P [a
tm]
Ignition Results in syngas Under SCO2 Conditions: 65% CO2 addition
With CO2 addition there is no significant pressure rise after ignition
Syngas /O2/CO2 Ignition Delay Time Measurements: Comparisons with Modeling
CO2=85%
12 Literature kinetic mechanisms tested
All mechanisms overpredict dataat high pressure !
0.78 0.79 0.80 0.81 0.82 0.83 0.84 0.85 0.86
100
1000
10000
100000Pavg= 40.374 atmConstant U,P = 0.11= 1.0XFuel= 0.10XCO2= 0.85
1000/T (K-1)
Aramco CRECK Davis FFCM GRI Kermones Li-2007 Li-2015 NUIG San Diego USC Varga Measured Data
Reaction Mechanism for sCO2
NSTC
28
Chemical Mechanism Development Summary
NSTC
• Combustion kinetics model refinement/development
• Existing kinetic models are only valid at low pressures < 50 atm
• We used multi-scale simulations to extend their validity to mixtures up to 300 bar by:
1. Quantum Mechanic simulations of the activation enthalpies in gas vs. CO2 environment
2. Molecular Dynamic simulations of reaction processes
29
Sensitivity Analysis
OH Sensitivity: Methane mixture 300 bar
Rxn#5: O2+H = O+OHRxn#26: H2O2+OH = H2O+HO2
Rxn#30: OH+HO2 = H2O+O2Rxn#31: OH+HO2 = H2O+O2
Rxn#32: 2HO2 = H2O2+O2Rxn#34: H+O2(+M) = HO2(+M)
Rxn#36: CO+OH = CO2+HRxn#46: CH4+OH = CH3+H2O
Rxn#47: CH4+HO2 = CH3+H2O2Rxn#49: CH3+HO2 = CH4+O2Rxn#90: CH3+O2 = CH3O+O
Rxn#91: CH3+O2 = CH2O+OHRxn#99: CH3+HO2 = CH3O+OH
Rxn#105: CH3O2+CH3 = 2CH3ORxn#153: CH2O+O2 = HCO+HO2Rxn#156: CH2O+OH = HCO+H2O
Rxn#157: CH2O+HO2 = HCO+H2O2Rxn#158: CH2O+CH3 = HCO+CH4
Rxn#194: 2CH3(+M) = C2H6(+M)Rxn#248: C2H4+OH = C2H3+H2O
-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0
Normalized OH Sensitivity
List
of R
eact
ions
NSTC
30
CH Sensitivity: Methane mixture at 300 barRxn#3: H2+OH = H+H2ORxn#4: 2O(+M) = O2(+M)
Rxn#5: O2+H = O+OHRxn#26: H2O2+OH = H2O+HO2
Rxn#30: OH+HO2 = H2O+O2Rxn#31: OH+HO2 = H2O+O2
Rxn#34: H+O2(+M) = HO2(+M)Rxn#36: CO+OH = CO2+HRxn#37: CO+OH = CO2+H
Rxn#43: CH3+H(+M) = CH4(+M)Rxn#44: CH4+H = CH3+H2
Rxn#46: CH4+OH = CH3+H2ORxn#47: CH4+HO2 = CH3+H2O2
Rxn#48: CH4+CH3O2 = CH3+CH3O2HRxn#49: CH3+HO2 = CH4+O2
Rxn#89: CH3+O2(+M) = CH3O2(+M)Rxn#90: CH3+O2 = CH3O+O
Rxn#91: CH3+O2 = CH2O+OHRxn#140: CH3O+O2 = CH2O+HO2
Rxn#174: CH3O(+M) = CH2O+H(+M)-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1
Normalized CH Sensitivity
List
of R
eact
ions
Sensitivity Analysis
NSTC
31 31
The important elementary steps in high-pressure C0-C4 fuel combustion
NSTCNaik, C. V.; Puduppakkam, K. V.; Meeks, E. J Eng Gas Turbines Power 2012, 134, 021504.
32
What is really happening during a reaction? Transition State Theory: 3-D potential energy surface
A+BC→ X≠ → AB+C
A+BCAB+C
X≠
X≠
Need collisions
NSTC
Figure adapted from Pilling and Seakins
NSTC
Gas-Phase Heat release Reaction CO+OH→CO2+H
Energy
Pathways shown for gas phase
NSTC
Effects of supercritical solvent within framework of Transition State Theory
NSTC
The supercritical solvent can modify predictions of this model in three ways: • changing the ability to reach the equilibrium by the
reactants and/or TS • shifting this equilibrium, and • changing probability of TS to convert to the products
NSTC
35
Elementary Reaction CO+OH→CO2+H (results with covalent CO2 addition as a spectator: new mechanism discovered !!)
NSTC
36
Elementary Reaction CO+OH→CO2+H (results with spectator CO2 molecule)
NSTC
37
Elementary Reaction of CO+OH→CO2+H (results with 1 additional spectator CO2)
Energy
• Pathways shown for CO2 autocatalytic effect published in J. Phys Chem A- Masunov & Vasu (2016)- above work
• CO2 opens up new pathways and accelerates heat release• Similar catalytic effects by CO2 seen in other reactions (HO2+HO2 → H2O2 + O2) but not in
H2CO + HO2 → HCO + H2O2
NSTC
38
Molecular Dynamic Study: CO+OH→CO2+H (results)
OVERALL REACTION: ∙OH + CO CO2 + H∙ (R1, k1)
Actually goes through these 3 reactions including HOCO intermediate
∙OH + CO HOCO∙ (R2, k2)
HOCO∙ ∙OH + CO (R2r, k-2)
HOCO∙ CO2 +H∙ (R3, k3)
32
321 kk
kkk
NSTC
39
Molecular Dynamic Study: CO+OH→CO2+H (results)
NSTC
40
Molecular Dynamic Study: CO+OH→CO2+H (results)
NSTC
41
Molecular Dynamic Study: CO+OH→CO2+H (results)
NSTC
42
Molecular Dynamic Study: CO+OH→CO2+H (results)
∙OH + CO CO2 + H∙
(R1, k1)
NSTC
43
Molecular Dynamic Study: CO+OH→CO2+H (results)
• CO2 molecules are among the most efficient to accelerate heat release reaction with pressure
• mixed quantum mechanics/molecular mechanics (QM/MM) theory level and molecular dynamics (MD) approach
NSTC
44
Task 5: CFD development and implementation in OpenFOAM• Real Gas Equations of State for sCO2
• Thermal properties for sCO2 combustor
• CFD simulation status
45
CFD Modeling DevelopmentA CFD code is being developed using an existing open source CFD program called
OpenFOAM, with the incorporation of a thermo-physical library and chemical kineticsmechanism that are applicable in the super critical regime. The resulting code will be ableto simulate reacting and non-reacting CO2 flow through a large range of thermodynamicconditions, as experienced in a theoretical super critical engine cycle.
This will entail 4 steps;1. Incorporate real gas equation of state.2. Incorporate a super critical thermodynamic library.3. Incorporate detailed sCO2 kinetic mechanism.4. Incorporate the non-premixed CMC turbulent combustion model.
Once the CFD code is validated for supercritical CO2 flows, sensitivity and design studieswill be performed on concept burners.
sCO2 CFD Modeling
46
Objective
Objective: To identify necessary thermal and transport models for sCO2combustor simulations and to calculate elementary thermal properties for sCO2 combustors.
• To find best equation of state for sCO2 combustor modeling.
• To develop a model for ‘compressibility factor’.
• To find best viscosity and thermal conductivity models.
• To quantify accurate elementary properties for sCO2 combustors.
47
The comparison of EOS for sCO2 and sO2:
• PRS is accurate for sCO2 and SRK is accurate for sO2.• The EOS has to be validate for mixtures of combustion.
48
Comparison of supercritical mixture viscosity mixture models:
• No reference data to compare.• Models predict within 10% of each other. • Preferred model is identified based on the computational time.
49
Comparison of supercritical mixture viscosity models:
Computational time (s)
0 5 10 15 20 25 30 35
Mix
ing
rule
Weighted Average
Wilkes Mixing rule
Lucas Mixing rule
Chung Mixing rule
Chung Mixing rule with Kij
Time
• Times are calculated for 100,000 cells.• Lucas et al., method is more suitable for detailed kinetic mechanisms and
LES or DNS simulations.
50
Thermal conductivity Mixture model
Chung et. al., Stiel and Thodos
Tim
e (s
)
0
10
20
30
40
50
Computational time
Comparison of supercritical mixture thermal conductivity models:
• Computational time calculated for 100,000 cells.• Stiel and Thodos is the least expensive computationally and suitable for LES
or DNS.
51
• Aramco 2.0 , CHEMKIN-RG and PCMC are coupled to investigate thermal properties of the sCO2 mixture.
• Soave-Redlich-Kwong EOS is identified as the better accurate EOS for modelling sCO2 combustion density.
Property Conclusions
• Several preliminary thermal properties of sCO2 combustor are quantified. A model is suggested for ‘Z’ in sCO2 combustor.
• Lucas et. al., method is identified as the accurate and computationally advantageous Viscosity correlation for sCO2 combustion.
• An accurate and inexpensive method is proposed by using Stieland Thodos thermal conductivity correlation.
52
Comparing conventional and supercritical combustion:
Simulated DLR-Jet
90m/s-300bar-CO2
90m/s-1bar-Air
OH
OH
• Simulation is performed with the premixed CMC in the OpenFOAM RANS CFD code.
• The current PCMC-OpenFOAM model is capable of using large mechanisms. The current simulation uses 493 species and 2,714 reactions.
• Stoichiometric CH4/O2 with 95% by mass CO2.
90m/s-300bar-CO2
90m/s-1bar-Air
Chemical Source Term (1/s)
Chemical Source Term (1/s)
53
Design strategy identified for future CFD simulation of dilution zone:
• Stoichiometric CH4/O2 with 95% CO2by mass. Half of the CO2 injected inthe PSR and the remainder added to thePFRs.
• Real gas code with detailed Aramcomechanism
Effect of mixing strategy on PFR emissionsMixing strategies in Dilution zone
54
Lean operating strategy identified
• Lean burn sCO2 reduces exit CO and shortens the reactor length.
55
Acknowledgement: DE‐FE0025260 (Dr. Seth Lawson as program manager)
Thank you, Questions?
Vasu Lab 2016
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