The plural of feedstock is feedstocks.

As in "the feedstocks are there".

petrochemicals, from crude oil feedstock

Yes! it does!

Even with the engine warmed the smell is still very noticeable.

It is related to the feedstock used, if oil-based feedstock is used then it will smell like "french fries".

If the feedstock is animal-based fat then it will smell like "pork" or "beef".

At least on my 1.9 TDi with catalytic converter.

the amount of feedstock avalialble

"Cellulosic" means that the material contains cellulose. Cellulose is found in wood, paper, grass and other plant matter. If it is used as a starting point for producing something, such as ethanol, that would make it a feedstock.