How TDAC reduces the number of scalar transport equations

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1. In YEqn.H (any combustion solver, e.g. chemFoam), the i-th scalar euqation is only solved when “composition.active(i)” is true. “composition” is an object of class “basicSpecieMixture”, which is defined in “CreateFields.H”: “basicSpecieMixture &composition = thermo.composition( )”
2. “basicSpecieMixture” is a class inherited from “basicMultiComponentMixture”, where the function “active” is defined. Initially, “active” of all the species will be put to be true.
3. When using TDAC, “TDACChemistryModel” will be used and when constructing “TDACChemistryModel”, a mechanism reduction method will be selected. At the same time, now “active” of all species will be put to false. Keep in mind that “standardChemistryModel” is constructed based on “thermo” and “TDACChemistryModel” is inherited from “standardChemistryModel”, the change on “active” is actually the change on thermo.composition( ).active.
4. After the mechanism reduction, the “active” of the important species will be put to true (see the setActive and active inline functions in TDACChemistryModelI.H). In this way, the “active” function in YEqn.H is also altered so that the inactive species transport equation will not be solved.