# 7.26. General Chemistry

This section is referenced in the following other sections

- Simulation Setup: General Chemistry Reference

## 7.26.1. General Chemistry

Scope

  Aria Material

    begin General Chemistry MechanismName

       Activation Energies {=} Value...

       Activation Temperature {=} Value

       Concentration Exponents For SpeciesName {=} Exponents...

       Deactivation Temperature {=} Value Action

       Deactivation Temperature Overshoot {=} Value

       Deactivation Temperature Rate {=} Value Action

       Enthalpy Of Formation For SpeciesName {=} Value

       Heats Of Reaction {=} Value...

       Newton Temperature Solve {=} Value

       Nucleation Time {=} Value

       Number Of Reactions {=} Value

       Phase Transfer Preserved Variable {=} Value

       Post Deactivation Gas Release {=} Value

       Post Deactivation Heat Release {=} Value

       Post Deactivation Release Time {=} Value

       Preexponential Factors {=} Value...

       Species Names {=} Value...

       Species Phases {=} Value...

       Species Variable Name {=} Value

       Steric Coefficients {=} Value...

       Stoichiometric Coefficients For SpeciesName {=} Coefficients...

       Temperature Phases {=} Value...

       Universal Gas Constant {=} Value

       begin Reaction ReactionName
       end

    end General Chemistry MechanismName

### 7.26.1.1. Line Commands

###### Activation Energies

Syntax

  Activation Energies {=} Value…

Summary

  Activation energy, E, for each Arrhenius-rate reaction

Description

  The units for this quantity may be whatever you like, as long as it results in a dimensionless quantity when combined with the temperature and universal gas constant.

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

###### Activation Temperature

Syntax

  Activation Temperature {=} Value

Summary

  Activation temperature

Description

  This specifies the activation temperature for general chemistry

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

###### Concentration Exponents For

Syntax

  Concentration Exponents For SpeciesName {=} Exponents…

Summary

  Concentration exponents, , for each reactant species for each Arrhenius rate reaction

Description

  Values of zero imply that the species is not a reactant in the specified reaction

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

###### Deactivation Temperature

Syntax

  Deactivation Temperature {=} Value Action

Summary

  Deactivation temperature

Description

  This specifies the deactivation temperature for general chemistry along with the deactivation action (terminate or continue)

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
Value | real | –
Action | string | –

###### Deactivation Temperature Overshoot

Syntax

  Deactivation Temperature Overshoot {=} Value

Summary

  Allowable overshoot for deactivation

Description

  This specifies the amount the temperature is allowed to overshoot the specified deactivation temperature without failing the timestep

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

###### Deactivation Temperature Rate

Syntax

  Deactivation Temperature Rate {=} Value Action

Summary

  Deactivation temperature rate

Description

  This specifies the deactivation temperature rate for general chemistry along with the deactivation action (terminate or continue)

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
Value | real | –
Action | string | –

###### Enthalpy Of Formation For

Syntax

  Enthalpy Of Formation For SpeciesName {=} Value

Summary

  Enthalpy of formation for each species

Description

  This specifies the enthalpy of formation at the reference temperature for each species. This should be in a consistent mass or mole-based unit system with the rest of the mechanism.

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

###### Heats Of Reaction

Syntax

  Heats Of Reaction {=} Value…

Summary

  Heat of reaction for each reaction

Description

  This specifies the heat of reaction at the reference temperature for each reaction. This should be in a consistent mass or mole-based unit system with the rest of the mechanism. Positive values represent an endothermic reaction and negative values represent an exothermic reaction.

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

###### Newton Temperature Solve

Syntax

  Newton Temperature Solve {=} Value

Summary

  Newton Temperature Solve

Description

  If set to true, use Newton’s method to solve for the temperature. Otherwise a constant heat capacity is assumed when calculating temperature.

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

###### Nucleation Time

Syntax

  Nucleation Time {=} Value

Summary

  Nucleation time to be used in rate calculations

Description

  If specified then all reaction rates will be scaled by .

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

###### Number Of Reactions

Syntax

  Number Of Reactions {=} Value

Summary

  Number of reactions in the chemical mechanism

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

###### Phase Transfer Preserved Variable

Syntax

  Phase Transfer Preserved Variable {=} Value

Summary

  Use isothermal phase transfers

Description

  Options are ‘temperature’ or ‘enthalpy’. This allows you to use temperature-preserving transfers of material from one phase to the other, rather than using enthalpy-preserving transfers (the default).

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

###### Post Deactivation Gas Release

Syntax

  Post Deactivation Gas Release {=} Value

Summary

  Gas release after deactivation

Description

  Specifies a uniform energy release to be applied after deactivation. The units of this value are moles per volume (e.g. mol/m3)

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

###### Post Deactivation Heat Release

Syntax

  Post Deactivation Heat Release {=} Value

Summary

  Heat release after deactivation

Description

  Specifies a uniform energy release to be applied after deactivation. The units of this value are energy per volume (e.g. J/m3)

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

###### Post Deactivation Release Time

Syntax

  Post Deactivation Release Time {=} Value

Summary

  Time for heat and gas release after deactivation

Description

  Specifies the time to use for the uniform heat and/or gas release terms.

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

###### Preexponential Factors

Syntax

  Preexponential Factors {=} Value…

Summary

  Pre-exponential factor, A, for each Arrhenius-rate reaction

Description

  Please note that this is the actual Arrhenius pre-exponential factor, A, and not the logarithm of the value (as was expected in the previous CHEMEQ capability).

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

###### Species Names

Syntax

  Species Names {=} Value…

Summary

  Names of all species participating in chemical mechanism

Description

  All of these names must be valid species defined elsewhere in the Material block (or in material phase sub-blocks).

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

###### Species Phases

Syntax

  Species Phases {=} Value…

Summary

  Name of the material phases for each chemical species

Description

  Provide the full name of the material phase for each chemical species, in the same order as the species are listed. If this command is omitted, then all species are assumed to not have a material phase.

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

###### Species Variable Name

Syntax

  Species Variable Name {=} Value

Summary

  Names of the input species variable to be used in rate calculations

Description

  If the chemical mechanism is formulated on a molar basis then this field must be in units of molar concentration (e.g. ), and if the mechanism is formulated on a mass basis then this field must be in units of mass concentration (e.g. ). If the solution variable is neither of these (e.g. mass fraction, mole fraction, etc.), then a material model to compute the required concentrations from the available solution variable must be provided.

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

###### Steric Coefficients

Syntax

  Steric Coefficients {=} Value…

Summary

  Steric coefficient exponent for each reaction

Description

  The steric coefficient has the form , where is the provided value. Zero will be assumed as the default for all reactions if this optional line command is not provided.

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

###### Stoichiometric Coefficients For

Syntax

  Stoichiometric Coefficients For SpeciesName {=} Coefficients…

Summary

  Stoichiometric coefficients, , for each reactant species for each reaction

Description

  These coefficients must sum to zero for each reaction if using a mass-based formulation.

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

###### Temperature Phases

Syntax

  Temperature Phases {=} Value…

Summary

  The material phase of the temperature to use for this reaction

Description

  In multi-material phase heterogeneous mechanisms, it is required to specify which phase’s temperature to use for each reaction.

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

###### Universal Gas Constant

Syntax

  Universal Gas Constant {=} Value

Summary

  Universal gas constant to be used in rate calculations

Description

  This is the standard universal gas constant, for use in the exponential term of the Arrhenius rate expression. The units must be consistent with the provided activation energy. If specifying an activation temperature () is preferred, then this can be set to 1 and activation temperatures can be provided for the activation energies.

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

## 7.26.2. Chemistry Solver Parameters For

Scope

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

Summary

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

    begin Chemistry Solver Parameters For ModelName

       Absolute Tolerance {=} absTol

       Chemistry Solver Algorithm {=} algorithmType

       Maximum Substeps {=} maxSubSteps

       Minimum Step Size {=} minStepSize

       Ode Solver {=} odeSolver...

       Relative Tolerance {=} relTol

    end Chemistry Solver Parameters For ModelName

### 7.26.2.1. 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

###### Chemistry Solver Algorithm

Syntax

  Chemistry Solver Algorithm {=} algorithmType

Summary

  This command specifies the coupling algorithm between the chemistry model and transport equations

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
algorithmType | string | COUPLED

###### 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 Step Size

Syntax

  Minimum Step Size {=} minStepSize

Summary

  Specifies the minimum integration step size.

Parameter | Value | Default
--- | --- | ---
{=} | {= | are | is} | –
minStepSize | real | 1e-30

###### Ode Solver

Syntax

  Ode Solver {=} odeSolver…

Summary

  This command selects the ODE solver to use for a segregated solve. For available options, refer to the ‘ODE Solvers’ section of this chapter.

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

###### 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