Setting species to QSS

Suppose you have a skeletal mechanism in Cantera's ctml format "mech_sk.xml", and that you want to set a number of species to QSS to create a reduced mechanism (either because you used a level of importance criterion like in H. Wu's 2019 PCI, or because someone did the analysis for you like with HyChem). You will need to modify "mech_sk.xml" to create "mech_red.xml".

1. Replace the <reactionArray> ... </reactionArray> field with

<reactionArray datasrc="#reaction_data">
    <skip species="undeclared" third_bodies="undeclared"/>
</reactionArray>

2. Add a new phase field below the existing one as follows:

<!-- phase QSS     -->
  <phase dim="3" id="QSS">
    <elementArray datasrc="elements.xml">O H C N</elementArray>
    <speciesArray datasrc="#species_data">
        QSS Species Here
    <skip element="undeclared"/>
  </speciesArray>
    <reactionArray datasrc="#reaction_data"/>
    <state>
      <temperature units="K">300.0</temperature>
      <pressure units="Pa">101325.0</pressure>
    </state>
   <thermo model="PengRobinsonGas"/>
    <kinetics model="GasQSSKinetics"/>
    <transport model="None"/>
    <phaseArray>gas</phaseArray>
  </phase>

Make sure to replace the field in <phaseArray> ... </phaseArray> with the name of the original (non-QSS) phase if it is not 'gas'. Replace 'QSS Species Here' with the QSS species separated with spaces, e.g. CH* HCO HCCO.

3. Remove the QSS species you added to the QSS phase from the non-QSS phase above.