responsibility to ensure that boundary conditions for both leading reactant and mixture fraction are specified correctly and that they are the same for both of them.
9. Exhaust gases present in EGR (Exhaust Gas Recirculation) systems are taken into account by defining active scalars for each exhaust gas species and solving additional transport equations for their mass fraction (see also Chapter 11, “Exhaust Gas Recirculation” in the Methodology volume).
Complex Chemistry Models
The complex chemistry model supports two types of format for reaction mechanism definition. One of them is the CHEMKIN format, the other the STAR-CD native format described below.
In order to use STAR-CD’s complex chemistry model, a reaction mechanism file called cplx.inp&& has to be created by the user for each chemical scheme in which a complex chemistry model is applied. The characters ‘&&’ at the end of the file name represent the chemical scheme number in which the complex chemistry model is applied. For example, if such a model is applied in chemical scheme no. 2, the reaction mechanism file should be called cplx.inp02. STAR will write an echo file cplx.inp&&-echo for each cplx.inp&& file it has read, so that users can ensure settings have been correctly applied.
File cplx.inp&& contains the reaction formula, chemical kinetic data and keywords and extra parameters for special reactions, as outlined below:
Reaction formula definition
The general form of a reaction formula is given by
Here, , , …, , , … are the stoichiometric coefficients which could be integer or real numbers, , , …, , , … are species names, , , …,
, , … are the mass fraction exponentials,Ais the pre-exponential factor (in units of cm-mole-sec-K),β the temperature exponent and E the activation energy of the Arrhenius rate constant (in cal/mol). If the mass fraction exponentials are equal to 1, they are not written into the corresponding echo file (cplx.inp&&-echo).
Rules:
• There are no spaces between stoichiometric coefficients , and species names. If or are equal to 1, they can be omitted.
• and must be separated by at least one space from the species name.
If the value of or is not specified, it will be assumed that =
or = .
• Character ‘=’ is used for reversible reactions; ‘⇒’ for irreversible reactions.
• There is no ‘+’ character between the pre-exponential factor, A, and the nearest species name. A,β and E are separated by at least one blank space.
• Everything following the ‘!’ character is treated as a comment
• The ‘+’ character should not be used in a real number expression. For example, 1.2E+05 should be written as 1.2E05.
• The maximum number of reactants or products in a single reaction must not exceed 5
Complex Chemistry Models
Three-body reaction definition
To define a three-body reaction, add a line starting with the keyword M after the reaction formula, i.e.
Rules:
• Keyword M must be enclosed by two ‘/’ characters and is not case sensitive
• A, B, … are species names and , , … are the corresponding efficiency factors. They are separated by at least one blank space.
The Landau-Teller reaction
To define a Landau-Teller reaction, add a line starting with the keyword RLT after the normal reaction formula, i.e.
Rules:
• Keyword RLT must be enclosed by two ‘/’ characters and is not case sensitive
• B and C are the Landau-Teller parameters and are separated by at least one blank space
• If the reaction is a three-body reaction as well, a new line is added starting with ‘ ’ and the third body efficiency factors
The Lindemann fall-off reaction
To define a Lindemann fall-off reaction, add a line starting with the keyword LOW after the reaction formula, i.e.
Rules:
• Keyword LOW must be enclosed by two ‘/’ characters and is not case sensitive
• , , and are the pre-exponential factor, temperature exponent and activation energy, respectively, of the low pressure limit and are separated each from each other by at least one blank space
• The corresponding values for the high pressure limit are assumed to be those given above as part of the reaction formula definition
• If the reaction is a three-body reaction as well, a new line is added starting with ‘ ’ and the third body efficiency factors
The Troe fall-off reaction
To define a Troe fall-off reaction, add two lines starting with keywords LOW and TROE, respectively, after the reaction formula, i.e.
/M/ A/α1/ B/α2/ …
α1 α2
/RLT / B C
/M/
/LOW / AL βL EL
AL βL EL
/M/
/LOW / AL βL EL
Complex Chemistry Models
Rules:
• The definition of keyword LOW is the same as above
• The pre-exponential factor, temperature exponent and activation energy values for the high pressure limit are assumed to be those given above as part of the reaction formula definition
• Keyword TROE must be enclosed by two ‘/’ characters and is not case sensitive
• a, b, c and d are the corresponding Troe parameters (d is optional)
• If the reaction is a three-body reaction as well, a new line is added starting with ‘ ’ and the third body efficiency factors.
The SRI fall-off reaction
To define a SRI fall-off reaction, add two lines starting with the keywords LOW and SRI, respectively, after the reaction formula, i.e.
Rules:
• The definition of keyword LOW is the same as above
• The pre-exponential factor, temperature exponent and activation energy values for the high pressure limit are assumed to be those given above as part of the reaction formula definition
• Keyword SRI must be enclosed by two ‘/’ characters and is not case sensitive
• a, b, c, d and e are the corresponding SRI parameters and are separated from each other by at least one blank space.
• If the reaction is a three-body reaction as well, a new line is added starting with ‘ ’ and the third body efficiency factors.
The Eddy Break-up reaction
To define an eddy break-up reaction in turbulent combustion, add a line starting with keywords EBU after the reaction formula, i.e.
Rules:
• Keyword EBU must be enclosed by two ‘/’ characters and is not case sensitive
• and are constansts appearing in the standard eddy break-up model, seeequation (10-8). If is not zero, the product will be included in the reaction rate calculation.
IOP is an integer determining which EBU model is being used:
IOP = 1 : Standard EBU model, reaction rate determined byequation (10-8)