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