There are a bunch of companies collecting used fry oil in this area and
concocting diesel.

This company claims to have ingredients in a bottle that can be added
to fry oil and simplify the process of converting it to diesel.

I doubt it very much, but then again Rudolph Diesel originally designed
his engine to run on vegetable oil, not pertroleum oil, so anything is
possible

http://www.dieselsecret.com/howitworks.html