Influence of
Chemistry Models and RCCE
on Computed Flame Behaviors
Guillaume Blanquart
Department of Mechanical Engineering
California Institute of Technology
Financial support:
Air Force Office of Sponsored Research (AFOSR)
Basic Research Initiative (BRI)
Jun-4-13
AFOSR Review Meeting
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Turbulent Combustion
• Turbulent  Transport
– Describe large scale 3D transport
– Predict turbulent dispersion
– Capture molecular mixing
Velocity
Vorticity
 Count in # of gridpoints
• Combustion  Chemistry
– Represent state of mixture
– Predict rate of change of state of mixture
 Count in # of species/reactions
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Plethora of Approaches
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A Great Opportunity
• Number of constraints
– Key element
Detailed Chemical
Kinetic Model
PES + RCCE
• Too many
 Go through 1D flames
– Same strategy as now
– Nothing new
1D Flames
• Just a few
 Direct integration
– DNS with RCCE
– New paradigm
Tabulation
Turbulent Flames
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Questions
• How to implement RCCE ?
– Constraints
– Coupling with CFD
• How much do we need ?
– Thermo properties
– Flame properties
– Flame structure
• Conditions
– Premixed flame
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RCCE for H2/O2 System
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RCCE – Constraints
• Observation #1 - Major species
– 3 major species: H2, O2, H2O
– 2 elemental conservation: H, O
 1 constraint
 Get all other major species right
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RCCE – Constraints
• Observation #2 - Heat Release
– Constant total enthalpy
– Function of
• Major species
• Temperature
 Get temperature right too
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RCCE – Constraints
• Observation #3 – Chemical source terms
– Source term for major species
• Depends on major species
• Depends on radicals: H, O, OH, HO2
 Constraint on radicals
Constraints: H2
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AFOSR Review Meeting
Constraints: H2, O, OH
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RCCE – Summary
• Constraints
–
–
–
–
Enthalpy
Pressure
H
O
– H2
– O, OH
– Rh
Reasons
Variations
1st thermo variable
2nd thermo variable
element conservation
element conservation
constant
constant
constant
constant
major species & temperature
major species chemical rates
radical chemical rates
unburnt to burnt
narrow range
very narrow range
Not
transported
Not transported
H2
O, OH
Temperature
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Comparison of Methods
Part I – 1D flame
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Chemistry Modeling
• Conditions
– Hydrogen-air
– Stoichiometric condition ( = 1)
– Unity Lewis transport.
• Four approaches (ordered by complexity)
– Detailed Kinetic Modeling (DKM): 9 species, 25 reactions.
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– Rate-Contr. Constr. Eq. (RCCE):
4 constraints, 3 transported scalars.
– Tabulated chemistry (flamelet):
1 progress variable (H2O).
– One-step/Arrhenius chemistry:
3 species, 1 reaction.
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1D Flame Structure
Same thermodynamic properties
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1D Flame Structure
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Comparison of Methods
Part II – 2D flame
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Vortex-Flame Interaction
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Regime Diagram
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Impact of Thermo Properties
• Configuration: Small, Fast vortex
All methods are the same
because same thermo props
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Impact of Flame Properties
• Configuration: Large, Slow vortex
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Impact of Flame Structure
• Configuration: Large, Fast vortex
Some deviations
but limited
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Relevance to
3D Turbulent & Hydrocarbons
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Turbulent Heptane Flame
• Chemistry
– Detailed : 35 species – 217 reactions
– Tabulated : 1 progress variable
– RCCE : not yet
• Turbulence
– High Karlovitz number: Ka=250
– Thin/Broken reaction zones regime
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Turbulent Heptane Flame
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Turbulent Heptane Flame
RCCE should capture
these fluctuations
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Summary
• RCCE has been implemented
– Coupled with CFD
– Tested in 1D flames
– Tested in 2D flames
• What matters?
1. Thermodynamic properties
2. Flame characteristics
3. Flame structure (to a lesser extend)
• What’s next?
– Implement RCCE with n-C3H8 & i-C4H10
• What constraints to use ?
– Test RCCE in turbulent flames
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Tabulated Chemistry
• Premixed flames
– Run a series of 1D flat flames
– Choose a progress variable
– Tabulate all properties with this variable
(C), (C)…
(Z,C),
(Z,C)…
• Diffusion flames
– Run a series of 1D counterflow flames
– Map all properties on mixture fraction
(Z), (Z)…
• Additional variables
– Heat losses/gains
• Add an enthalpy variable
H
– Background compression
• Add pressure
• Final tabulation
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P
(Z,C,H,P), (Z,C,H,P)…
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Tabulated Chemistry
(Z, C, H, P)
• Final tabulation
Pressure
Thermodynamic state
Mixture fraction
 Mixture composition
 How much of H, C, O
Enthalpy
 Total energy in mixture
 Chemical + sensible
Progress variable
 Extent of reaction
 Similar to temperature
Chemical
energy
• What is RCCE ?
– E = Equilibrium calculation
• At a given thermodynamic state  H,P
– C = Constrained by
• Elemental mass fractions  Z
• Other species concentrations  Ci
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AFOSR Review Meeting
RCCE is similar to
chemistry tabulation
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