# 7.20. CHEMEQ

This section is referenced in the following other sections

- Simulation Setup: CHEMEQ Reference

## 7.20.1. Parameters For Chemeq Model

Scope

  Aria Material, Material Phase

Summary

  Parameters for the CHEMEQ chemistry model within Aria. The ModelName must appear in a SRC term for an ENERGY equation in order to be applied.

    begin Parameters For Chemeq Model ModelName

       Activation Energies {=} activation energies...

       Activation Energy St Devs {=} activation energy st devs...

       Aux Variable Names {=} aux variable names...

       Aux Variable Subroutine {=} aux variable subroutine

       Concentration Exponents For SpeciesName {=} Exponents...

       Concentration Units {=} concentration units...

       Condensed Fraction {=} condensed fraction

       Energy Release Units {=} {per unit mass | per unit volume}

       Energy Releases {=} energy releases...

       Enthalpies Of Formation {=} enthalpies of formation...

       Extent Of Reaction Based On extent of reaction based on...

       Log Preexponential Factors {=} log preexponential factors...

       Number Of Reactions {=} number of reactions

       Pressure {=} pressure...

       Pressure Exponents {=} pressure exponents...

       Rate Multiplier {=} rate multiplier...

       Reaction Rate Model {=} reaction rate model

       Reaction Rate Subroutine {=} reaction rate subroutine

       Reference Pressure {=} reference pressure

       Species Molecular Weights {=} species molecular weights...

       Species Names {=} species names...

       Species Phases {=} species phases...

       Steric Coefficients {=} steric coefficients...

       Stoichiometric Coefficients For SpeciesName {=} Exponents...

       begin Reaction ReactionName
       end

    end Parameters For Chemeq Model ModelName

### 7.20.1.1. Line Commands

###### Activation Energies

Syntax

  Activation Energies {=} activation energies…

Summary

  This command specifies the activation energies for each reaction.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
activation energies | real… | –

###### Activation Energy St Devs

Syntax

  Activation Energy St Devs {=} activation energy st devs…

Summary

  This command supplies the standard deviations for the activation energies for each reaction. The order is significant, and corresponds to the order in which the Reactions are specified.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
activation energy st devs | real… | –

###### Aux Variable Names

Syntax

  Aux Variable Names {=} aux variable names…

Summary

  Supplies the names for any auxiliary variables. The number of auxiliary variables is implied by the size of this list.

Description

  Warning

  This command is deprecated and should not be used any more.

  The entries must be separated by whitespace, without commas. These variables do not participate in the reaction kinetics, but are derived from the species variables and calculated in the user-defined subroutine named via the “AUX VARIABLE SUBROUTINE NAME” line command.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
aux variable names | string… | –

###### Aux Variable Subroutine

Syntax

  Aux Variable Subroutine {=} aux variable subroutine

Summary

  Supplies the name of the user-defined subroutine that performs any auxiliary variable calculations. This command is required if auxiliary variables are named.

Description

  Warning

  This command is deprecated and should not be used any more.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
aux variable subroutine | string | –

###### Concentration Exponents For

Syntax

  Concentration Exponents For SpeciesName {=} Exponents…

Summary

  For the given species, this command specifies the concentration exponents for each reaction.

Parameter | Value | Default
--- | --- | ---
SpeciesName | string | –
{=} | {= | are | is} | –
Exponents | real… | –

###### Concentration Units

Syntax

  Concentration Units {=} concentration units…

Summary

  Specifies the concentration units.

Description

  Specifies the concentration units. This input is required when using a pressurization model or using the `FROM_CHEMEQ` model.

  Valid inputs for the four concentration types include:

  > - `Mass Fraction` or `Mass Fractions`

  > - `Mole Fraction` or `Mole Fractions`

  > - `Mass` or `Density`

  > - `Moles` or `Molar`

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
concentration units | string… | UNKNOWN_UNITS

###### Condensed Fraction

Syntax

  Condensed Fraction {=} condensed fraction

Summary

  Specifies mass fraction of the condensed phase.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
condensed fraction | real | –

###### Energy Release Units

Syntax

  Energy Release Units {=} {per unit mass | per unit volume}

Summary

  Specifies the energy release units for each reaction, PER VOLUME or PER UNIT MASS.

  Default is PER VOLUME. If PER UNIT MASS is selected, the specified heat release value is multiplied by the local density.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
energy release units | {per unit mass | per unit volume} | PER VOLUME

###### Energy Releases

Syntax

  Energy Releases {=} energy releases…

Summary

  This command specifies the energy release for each reaction.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
energy releases | real… | –

###### Enthalpies Of Formation

Syntax

  Enthalpies Of Formation {=} enthalpies of formation…

Summary

  This command specifies the enthalpies of formation for each species

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
enthalpies of formation | real… | –

###### Extent Of Reaction Based On

Syntax

  Extent Of Reaction Based On extent of reaction based on…

Summary

  This command supplies the species on which the progress variable for each distributed activation energy depends. The order is significant, and corresponds to the order in which the Reactions are specified.

Parameter | Value | Default
--- | --- | ---
extent of reaction based on | string… | –

###### Log Preexponential Factors

Syntax

  Log Preexponential Factors {=} log preexponential factors…

Summary

  This command specifies the natural logarithms of the pre-exponential factors for each reaction.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
log preexponential factors | real… | –

###### Number Of Reactions

Syntax

  Number Of Reactions {=} number of reactions

Summary

  Specifies the number of reactions for this material.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
number of reactions | integer | –

###### Pressure

Syntax

  Pressure {=} pressure…

Summary

  Specifies the expression for pressure for this material.

Description

  Specifies the expression for pressure for this material. The preferred option is to use `Pressure = From_Material_Definition` and put a pressure specification in the material block (e.g. `Pressure = Pressurization_Model`). If you are using pressurization zones, you must use this approach. Using `Pressure = Pressurization_Model` here will generate an error.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
pressure | string… | –

###### Pressure Exponents

Syntax

  Pressure Exponents {=} pressure exponents…

Summary

  This command specifies the pressure exponents for each reaction.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
pressure exponents | real… | –

###### Rate Multiplier

Syntax

  Rate Multiplier {=} rate multiplier…

Summary

  Specifies a generic expression for the rate multiplier for this ChemEq model. This input is optional, and the rate multiplier defaults to 1.0 if this is omitted.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
rate multiplier | string… | 1

###### Reaction Rate Model

Syntax

  Reaction Rate Model {=} reaction rate model

Summary

  By default, reaction rates are Arrhenius. If this line command is included, then a named reaction rate model can be used. Current options are: “Prout_Tompkins”

Description

  Warning

  This command is deprecated and should not be used any more.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
reaction rate model | string | –

###### Reaction Rate Subroutine

Syntax

  Reaction Rate Subroutine {=} reaction rate subroutine

Summary

  By default, reaction rates are Arrhenius. If this line command is included, then the named subroutine is called instead.

Description

  Warning

  This command is deprecated and should not be used any more.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
reaction rate subroutine | string | –

###### Reference Pressure

Syntax

  Reference Pressure {=} reference pressure

Summary

  Specifies the reference pressure for this material.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
reference pressure | real | –

###### Species Molecular Weights

Syntax

  Species Molecular Weights {=} species molecular weights…

Summary

  Supplies the molecular weight for each chemical species. The order is significant, and corresponds to the order in which the Species Names are specified.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
species molecular weights | real… | –

###### Species Names

Syntax

  Species Names {=} species names…

Summary

  Supplies names for the chemical species. The number of chemical species is implied by the size of this list. The entries must be separated by whitespace, without commas.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
species names | string… | –

###### Species Phases

Syntax

  Species Phases {=} species phases…

Summary

  Supplies the phase for each chemical species. The order is significant, and corresponds to the order in which the Species Names are specified.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
species phases | {condensed | gas} | –

###### Steric Coefficients

Syntax

  Steric Coefficients {=} steric coefficients…

Summary

  This command specifies the steric coefficients for each reaction.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
steric coefficients | real… | –

###### Stoichiometric Coefficients For

Syntax

  Stoichiometric Coefficients For SpeciesName {=} Exponents…

Summary

  For the given species, this command specifies the stoichiometric coefficients for each reaction.

Parameter | Value | Default
--- | --- | ---
SpeciesName | string | –
{=} | {= | are | is} | –
Exponents | real… | –

## 7.20.2. Chemeq Solver For

Scope

  Aria Region, Equation System, Explicit Equation System, Root Finder Equation System

Summary

  Parameters for the CHEMEQ solver applicable to the previously defined material with CHEMEQ model ModelName. The CHEMEQ SOLVER model produces no independent action since the ModelName must first appear in a SRC term for an ENERGY equation before it be applied.

    begin Chemeq Solver For ModelName

       Absolute Tolerance {=} absTol

       Activation Temperature {=} T_act

       Activation Temperature Rate {=} T_dot

       Activation Time {=} T_init

       Allow Old Heat Generation Method {=} {false | no | off | on | true | yes}

       Asymptotic Tolerance {=} Tol

       Aux Variable Name {=} C_init

       Chemistry Step Multiplier {=} Dt_cond_over_dt_chem

       Deactivation Temperature {=} t {continue | terminate}

       Deactivation Temperature Overshoot {=} dT_overshoot

       Deactivation Temperature Rate {=} T_dot {continue | terminate}

       Deactivation Time {=} T_stop {continue | terminate}

       Enable Enthalpy Integration

       Epsilon Max {=} E_max

       Epsilon Min {=} E_min

       Maximum Substeps {=} maxSubSteps

       Minimum Chemistry Timestep {=} Dt_min

       Minimum Concentration For Name {=} C_min

       Ode Solver {=} odeSolver...

       Percentage Asymptotics {=} PercentValue

       Post Deactivation Gas Release {=} gasRelease

       Post Deactivation Heat Release {=} heatRelease

       Post Deactivation Release Time {=} releaseTime

       Rate Limiter Factor {=} rateLimiterFactor

       Relative Tolerance {=} relTol

       Species Name {=} Conc

    end Chemeq Solver For ModelName

### 7.20.2.1. Line Commands

###### Absolute Tolerance

Syntax

  Absolute Tolerance {=} absTol

Summary

  Specifies the absolute solution tolerance for the ODE solver

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
absTol | real | 1e-12

###### Activation Temperature

Syntax

  Activation Temperature {=} T_act

Summary

  Specification of threshold activation temperature for chemistry.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
T_act | real | 0.0

###### Activation Temperature Rate

Syntax

  Activation Temperature Rate {=} T_dot

Summary

  Specification of temperature rate limit (dT/dt) for which chemistry activation occurs.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
T_dot | real | REAL_MAX

###### Activation Time

Syntax

  Activation Time {=} T_init

Summary

  Specification of activation time for chemistry.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
T_init | real | REAL_MAX

###### Allow Old Heat Generation Method

Syntax

  Allow Old Heat Generation Method {=} {false | no | off | on | true | yes}

Summary

  This command has been removed, using it will result in an error.

Description

  Warning

  This command is deprecated and should not be used any more.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
Bool | {false | no | off | on | true | yes} | FALSE

###### Asymptotic Tolerance

Syntax

  Asymptotic Tolerance {=} Tol

Summary

  Specifies the asymptotic selection criterion for the chemical rate equations.

Description

  Warning

  This command is deprecated and should not be used any more.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
Tol | real | 100.0

###### Aux Variable

Syntax

  Aux Variable Name {=} C_init

Summary

  Specifies the initial value for the named auxiliary variable.

Description

  Warning

  This command is deprecated and should not be used any more.

Parameter | Value | Default
--- | --- | ---
Name | string | –
{=} | {= | are | is} | –
C_init | real | 0.0

###### Chemistry Step Multiplier

Syntax

  Chemistry Step Multiplier {=} Dt_cond_over_dt_chem

Summary

  This command specifies the ratio of the maximum allowed conduction timestep to the smallest, current chemistry time step.

Description

  Warning

  This command is deprecated and should not be used any more.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
Dt_cond_over_dt_chem | real | 100.0

###### Deactivation Temperature

Syntax

  Deactivation Temperature {=} t {continue | terminate}

Summary

  Specification of deactivation temperature and how the simulation should proceed after deactivation.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
t | real | REAL_MAX
ChemistryDeactivationAction | {continue | terminate} | TERMINATE

###### Deactivation Temperature Overshoot

Syntax

  Deactivation Temperature Overshoot {=} dT_overshoot

Summary

  Specification of acceptable overshoot of the deactivation temperature for the limiting procedure

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
dT_overshoot | real | 1.0

###### Deactivation Temperature Rate

Syntax

  Deactivation Temperature Rate {=} T_dot {continue | terminate}

Summary

  Specification of temperature rate limit (T_dot) for deactivation and how the simulation should proceed after deactivation.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
T_dot | real | REAL_MAX
ChemistryDeactivationAction | {continue | terminate} | TERMINATE

###### Deactivation Time

Syntax

  Deactivation Time {=} T_stop {continue | terminate}

Summary

  Specification of deactivation time for chemistry and how the simulation should proceed after deactivation.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
T_stop | real | REAL_MAX
ChemistryDeactivationAction | {continue | terminate} | TERMINATE

###### Enable Enthalpy Integration

Syntax

  Enable Enthalpy Integration

Summary

  This command has been removed, using it will result in an error.

Description

  Warning

  This command is deprecated and should not be used any more.

###### Epsilon Max

Syntax

  Epsilon Max {=} E_max

Summary

  Specifies the upper bound convergence criterion and chemistry time scale check.

Description

  Warning

  This command is deprecated and should not be used any more.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
E_max | real | 10.0

###### Epsilon Min

Syntax

  Epsilon Min {=} E_min

Summary

  Specifies the lower bound convergence criterion and chemistry time scale check.

Description

  Warning

  This command is deprecated and should not be used any more.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
E_min | real | 0.0001

###### Maximum Substeps

Syntax

  Maximum Substeps {=} maxSubSteps

Summary

  Specifies the maximum number of chemistry substeps per global time step.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
maxSubSteps | integer | 100000

###### Minimum Chemistry Timestep

Syntax

  Minimum Chemistry Timestep {=} Dt_min

Summary

  Specifies the minimum time step allowed during the solution of the chemical rate equations.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
Dt_min | real | 1.0e-15

###### Minimum Concentration For

Syntax

  Minimum Concentration For Name {=} C_min

Summary

  Specifies the minimum concentration for the named species.

Description

  Warning

  This command is deprecated and should not be used any more.

Parameter | Value | Default
--- | --- | ---
Name | string | –
{=} | {= | are | is} | –
C_min | real | 1.0e-12

###### Ode Solver

Syntax

  Ode Solver {=} odeSolver…

Summary

  This command selects the ODE solver to use for the CHEMEQ solve.

Description

  For available options, refer to the ‘ODE Solvers’ section in the ‘Chemistry’ chapter of the user manual. This command is required to activate an ODE solver.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
odeSolver | string… | NONE

###### Percentage Asymptotics

Syntax

  Percentage Asymptotics {=} PercentValue

Summary

  Specifies the percentage of the chemical rate equations that will always be solved using asymptotics.

Description

  Warning

  This command is deprecated and should not be used any more.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
PercentValue | real | 0.0

###### Post Deactivation Gas Release

Syntax

  Post Deactivation Gas Release {=} gasRelease

Summary

  Amount of gas to be released uniformly after deactivation (units are always in moles per volume).

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
gasRelease | real | 0.01

###### Post Deactivation Heat Release

Syntax

  Post Deactivation Heat Release {=} heatRelease

Summary

  Amount of energy to be released uniformly after deactivation. The units must be consistent with the base ChemEq heat release units (energy per volume or energy per mass).

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
heatRelease | real | 0.01

###### Post Deactivation Release Time

Syntax

  Post Deactivation Release Time {=} releaseTime

Summary

  Time after deactivation for constant heat and gas sources to be active

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
releaseTime | real | 0.01

###### Rate Limiter Factor

Syntax

  Rate Limiter Factor {=} rateLimiterFactor

Summary

  Enables a rate limiter and specifies what fraction of the fluid time step to consider for the limiter time step.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
rateLimiterFactor | real | 0.01

###### Relative Tolerance

Syntax

  Relative Tolerance {=} relTol

Summary

  Specifies the relative solution tolerance for the ODE solver

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
relTol | real | 1e-6

###### Species

Syntax

  Species Name {=} Conc

Summary

  Specifies the initial concentration for the named species.

Parameter | Value | Default
--- | --- | ---
Name | string | –
{=} | {= | are | is} | –
Conc | real | 0.0