Cantera/CTI Files

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

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')
                )

Reaction Specification

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.

Arrhenius 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) $

So, for 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])

Coverage-Dependent Surface Rates

The reaction rate may have some kind of... I dunno... coverage dependency, I guess?

I'm still working through this. 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

Sticking Equations

No idea how this works.

surface_reaction( "OH + PT(S) => OH(S)",   stick(1.00000E+00, 0, 0))

Duplicate Reactions

surface_reaction( "O2 + 2 PT(S) => 2 O(S)",   Arrhenius(1.80000E+21, -0.5, 0),
                  options = 'duplicate')