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Generating And Using a Fuel Rich RPA Thermo Database

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ferram4 edited this page Jul 31, 2017 · 1 revision

As noted by Kauffmann et al, RPA's chemical equilibrium calculator gives erroneous results when run extremely fuel-rich with carbon-containing fuels. The calculator cracks carbon chains down into methane, ethane, their derivatives, and a large amount of graphite; this is the result of the calculator working solely by maximizing the entropy of the resulting chemical equilibrium under the assumption that activation energy for reactions can be ignored (in fact, the calculator has no concept of reactions themselves). Therefore, we must create a modified thermo database for the calculator to use for fuel-rich situations. As of this writing, I am not sure if the RPA Lite license allows modification + redistribution of the thermo database (it does allow pure redistribution, but does not mention modification) and so we will take this approach for now.

Open RPA and go to the Thermodynamic Database tab. Check the Products box and select Show Both. Then, click Save As and save a backup copy of the database to the Resources directory; name it something like ThermoStd.inp. Use the Filter to track down the following species and remove them:

  • C(gr) - solid graphite
  • CH4 - gaseous methane
  • CH3 - gaseous ammonia
  • CH3OH - gaseous methanol
  • CH3O - gaseous methoxide
  • CH3CHO - gaseous ethanal
  • CH3CO - gaseous acetyl radical
  • C2H2,acetylene - gaseous acetylene
  • C2H2,vinylidene - gaseous vinylidene group
  • C2H4 - gaseous ethylene
  • C2H4O - gaseous ethylene oxide
  • C2H5OH - gaseous ethanol
  • C2H6 - gaseous ethane

After doing this, click Save As and save this database as ThermoRich.inp. You should now have Thermo.inp (unchanged) ThermoStd.inp (backup) and ThermoRich.inp (changed) in the database. Thermo.inp is the database that RPA loads.

To swap between the databases go to the Resources directory, delete Thermo.inp, make a copy of the standard or rich database, and rename that copy to Thermo.inp. Then, in RPA in the Thermodynamic Database tab, click Reload and the database will be updated. You can confirm you are using the correct database by filtering for C(gr) and seeing if it appears.

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