It is the inoxidizable and nonvolatile remnant. Mostly metallic and for the most part originates from lubricant additives like Calcium and Zinc. Soot is the typical term for carbonaceous material that combusted in the regen cycle. If you want to say ash is a byproduct of soot regeneration, you are lumping this carbonaceous material and the metallic material into one thing and calling it soot. It's just semantics but I think we agree on the concept.
Originally Posted by BBDartCA
Ash is a byproduct from soot regeneration.