Allow third-body PLOG and Chebyshev reactions

[kyleniemeyer]

Abstract

Cantera currently does not allow third-body PLOG or Chebyshev reactions. For PLOG, attempting this raises an error when processing the YAML file, and for Chebyshev it raises a DepracationWarning and then ignores any third-body effects.

Motivation

Although the original motivation for this behavior may have been to emulate how Chemkin handled (i.e., ignored) third-body effects in PLOG and Chebyshev reactions, Cantera's current behavior does not allow users to specify third-body PLOG or CHEB reactions when that is their intent.

If someone includes a PLOG reaction H + O2 + M <=> O + OH + M, plus any specific third-body efficiencies, it's reasonable to expect the rate to be calculated as [H][O2][M]kf(T,P).

Current behavior:

Including + M in a PLOG reaction raises the error Found superfluous 'M' in pressure-dependent-Arrhenius reaction..

Interestingly, including + M in a Chebyshev reaction just raises DeprecationWarning: Chebyshev reaction equation: Specifying 'M' in the reaction equation for Chebyshev reactions is deprecated., rather than an error. However, my testing shows that third-body efficiencies are ignored.

Possible Solutions

Removing the check for third-body PLOG and Chebyshev reactions, and also making sure to incorporate any third-body effects when calculating the rate.

The docs should also probably mention this.

References

https://groups.google.com/g/cantera-users/c/wq_DxTFWnLc/m/6mbFN6YeAwAJ?pli=1