Cantera/CTI Files
From charlesreid1
CTI = CanTera Input file
CTI files use a custom markup language to specify information about the kinetics.
Division of CTI Files
The file can be divided into multiple parts:
- Phase specification
- Species
- Gas species
- Surface species
- Reactions
- Gas reactions
- Surface reactions
Units Specification
The units are the first thing defined in the file:
units(length = "cm", time = "s", quantity = "mol", act_energy = "J/mol")
Phase Specification
Gas
ideal_gas(name = "gas",
elements = "O H C N Ar",
species = """gri30: H2 H O O2 OH
H2O HO2 H2O2
C CH CH2 CH2(S) CH3 CH4 CO CO2
HCO CH2O CH2OH CH3O CH3OH C2H C2H2 C2H3
C2H4 C2H5 C2H6 HCCO CH2CO HCCOH AR N2""",
transport = 'Mix',
reactions = 'gri30: all',
options = ['skip_undeclared_elements',
'skip_undeclared_species'],
initial_state = state(temperature = 300.0, pressure = OneAtm,
mole_fractions = 'CH4:0.095, O2:0.21, AR:0.79')
)
Interface (Surface)
ideal_interface(name = "Pt_surf",
elements = " Pt H O C ",
species = """ PT(S) H(S)
H2O(S) OH(S) CO(S) CO2(S) CH3(S)
CH2(S)s CH(S) C(S) O(S) """,
phases = "gas",
site_density = 2.7063e-9,
reactions = "all",
initial_state = state(temperature = 900.0,
coverages = 'O(S):0.0, PT(S):0.5, H(S):0.5')
)
Species Specification
species(name = "CH3OCHO",
atoms = " C:2 H:4 O:2 ",
thermo = (
NASA( [ 300.00, 1452.00], [ 2.435262000E+00, 1.819483250E-02,
1.912365900E-06, -8.442489450E-09, 2.617589100E-12,
-4.465147320E+04, 1.495222650E+01] ),
NASA( [ 1452.00, 5000.00], [ 1.065691850E+01, 9.381127230E-03,
-3.376772060E-06, 5.424555960E-10, -3.222953300E-14,
-4.846517580E+04, -3.275794430E+01] )
),
transport = gas_transport(
geom = "nonlinear",
diam = 4.037,
well_depth = 395,
dipole = 1.3,
rot_relax = 1),
note = "4/15/ 8 THERM"
)
Reaction Specification
Gas Reactions
An example gas reaction CTI file is located at cantera/data/inputs/h2o2.cti.
In general, the gas phase reaction rate can be modeled as:
$ r_{j} = k_j \sum_{i} \nu_{ij} c_{i}^{n_{ij}} $
where $ \nu_{ij} $ is the stoichiometric coefficient for species i in reaction j, $ c_i $ is the molar concentration of species i, and $ n_{ij} $ is the order of reaction j with respect to species i.
Arrhenius Gas Kinetics
The standard way to model reaction kinetics in the gas phase is to use Arrhenius kinetics. This models the reaction rate constant $ k_j $ as:
$ k_j = A_j T^{b_j} \exp \left( - \dfrac{ E_j }{ RT } \right) $
where the Arrhenius reaction parameters are:
- $ A_j $ - Arrhenius parameter pre-exponential factor
- $ b_j $ - Arrhenius parameter, degree of temperature influence on kinetic rate constant
- $ E_j $ - Arrhenius parameter, activation energy of reaction
These quantities can be specified in a CTI file as follows:
reaction( "A + B => C + D", [A, b, E] )
and the units of each are:
- $ A_j $ - specified in units of $ \frac{ \text{cm}^3 }{ \text{mol} \cdot \text{s} } $
- $ b_j $ - dimensionless
- $ E_j $ - specified in units of $ \frac{ \text{cal} }{ \text{mol} } $
Arrhenius Gas Kinetics Example
Example:
Specify the reaction
$ \text{H} + \text{O}_2 \rightarrow \text{O} + \text{OH} $
which has the following parameter values:
$ A = 3.54700E+15 \quad \frac{ \text{cm}^3 }{ \text{mol} \cdot \text{s} } $
$ b = -0.406 $
$ E = 16599 \quad \frac{ \text{cal} }{ \text{mol} } $
Result:
reaction( "H + O2 <=> O + OH", [3.54700E+15, -0.406, 16599])
Arrhenius Gas Kinetics Code
More information on what blocks of code process this stuff from the CTI file.
Three-Body Gas Reactions
A three body gas reaction is... I don't know.
three_body_reaction( "H2 + M <=> H + H + M", [4.57700E+19, -1.4, 104380],
efficiencies = " AR:0 CO:1.9 CO2:3.8 H2:2.5 H2O:12 HE:0 ")
Three Body Gas Reactions Example
It would help if I could figure out what this reaction type is, before putting together an example.
Three Body Gas Reactions Code
When Cantera processes a CTI file, it determines what kind of kinetics object to use. If the kinetics is for a gas phase, the object is a GasKinetics object. The GasKinetics object has a GasKinetics::addReaction() method, which is run for each reaction in the CTI file:
void GasKinetics::
addReaction(ReactionData& r)
{
switch (r.reactionType) {
case ELEMENTARY_RXN:
addElementaryReaction(r);
break;
case THREE_BODY_RXN:
addThreeBodyReaction(r);
break;
case FALLOFF_RXN:
addFalloffReaction(r);
break;
case PLOG_RXN:
addPlogReaction(r);
break;
case CHEBYSHEV_RXN:
addChebyshevReaction(r);
break;
default:
throw CanteraError("GasKinetics::addReaction", "Invalid reaction type specified");
}
The three body reaction computation is set up in GasKinetics::addThreeBodyReaction:
void GasKinetics::
addThreeBodyReaction(ReactionData& r)
{
// install rate coeff calculator
size_t iloc = m_rates.install(reactionNumber(), r);
// add constant term to rate coeff value vector
m_rfn.push_back(r.rateCoeffParameters[0]);
// forward rxn order equals number of reactants + 1
m_fwdOrder.push_back(r.reactants.size() + 1);
m_3b_concm.install(reactionNumber(), r.thirdBodyEfficiencies,
r.default_3b_eff);
registerReaction(reactionNumber(), THREE_BODY_RXN, iloc);
}
Falloff Gas Reactions
falloff_reaction( "H + O2 (+ M) <=> HO2 (+ M)",
kf = [1.47500E+12, 0.6, 0],
kf0 = [6.36600E+20, -1.72, 524.8],
falloff = Troe(A = 0.8, T3 = 1e-30, T1 = 1e+30),
efficiencies = " CO:1.9 CO2:3.8 H2:2 H2O:11 O2:0.78 ")
Falloff Gas Reaction Example
Falloff Gas Reaction Code
Other Gas Reaction Options
Duplicate is the only option I see:
reaction( "HO2 + HO2 <=> H2O2 + O2", [1.30000E+11, 0, -1629.3],
options = ["duplicate"])
Surface Reactions
Any surface reaction can be specified in the cti file using the surface_reaction function. The usage depends on the surface reaction form.
There are a variety of forms of surface reactions, each with a different specification method.
An example surface reaction CTI file is located at cantera/data/inputs/ptcombust.cti.
Arrhenius Surface Kinetics
The plain/default way, which uses Arrhenius kinetics:
surface_reaction( "A(s) => B(s) + C", [A, b, E])
where:
- A(s), B(s), C - species whose properties are defined in the species section (see above)
- A - Arrhenius parameter, pre-exponential factor (specified in units of...)
- b - Arrhenius parameter, degree of temperature influence on kinetic rate constant
- E - Arrhenius parameter, activation energy of reaction
The Arrhenius expression is:
$ k = A T^b \exp \left( \frac{E}{RT} \right) $
Arrhenius Surface Kinetics Example
A catalytic reaction where H2O (adsorbed onto a platinum surface) desorbs would look like this:
surface_reaction( "H2O(S) => H2O + PT(S)", [1.00000E+13, 0, 40300])
Arrhenius Surface Kinetics Code
Not sure where this is dealt with in the Cantera code.
Surface Reactions with Coverage-Dependent Rates
Still working through this coverage dependency.
This uses some kind of expression containing a, m, and e.
surface_reaction( "A(s) => B(s) + C", Arrhenius(A, b, E, coverage=['A(s)', surface_a, surface_m, surface_e])
Attempting to uncover how this is dealt with:
importKinetics::getCoverageDependence() rdata.cov vector contains coverage-related parameters/information rdata.cov.push_back(species_index) rdata.cov.push_back(a) rdata.cov.push_back(m) rdata.cov.push_back(e)
and then
InterfaceKinetics::addElementaryReaction
if r.cov.size > 3:
this rxn is dependent on coverage
register rxn
Surface Reactions with Sticking Equations
No idea how this works.
surface_reaction( "OH + PT(S) => OH(S)", stick(1.00000E+00, 0, 0))
Surface Reactions with Falloff
No idea.
Surface Reactions with Duplicate Reactions
surface_reaction( "O2 + 2 PT(S) => 2 O(S)", Arrhenius(1.80000E+21, -0.5, 0),
options = 'duplicate')