Judy Cooper
Ansys Employee

Hi Meshack:

Unfortunately, there is no simple answer here.  Combining mechanisms that aren't necessarily interoperable could create a numerically stiff system...  For instance, joining arbitrary mechanisms may set up unrealistic competing reactions, (because the rates of certain reactions are no longer correct in the new context), which creates numerical instability.

Most mechanisms for soot are derived for a specific context and precursor specie(s); they were developed for and work well with their base combustion mechanisms.  It would probably be best to research the background of your third-party soot mechanism to find out how it came to be developed, and the conditions under which it was tested and found to work well. Soot mechanisms are not a standalone thing and are often an add-on to a prexisting chemistry mechanism. Certainly, they depend on certain precursor species to be present in the base mechanism to work properly.