To run a diesel on renewable fuel you need biodiesel or you can (with a whole mess of caveats) feed it straight vegetable oil once the oil and engine are hot.

Biodiesel is not sold very many places, but you can make it yourself from vegetable oil, and some other stuff.

Biodieselgear makes little processing plants that make pretty much the kind of quantities I’m going to be looking to make.

Journytoforever.org has a whole bunch of good links on the subject, including a firm that makes complete conversion kits (pricey) as well as a german company that makes a computer that dynamically mixes bio/reg diesel with vegetable oil - BioCar. The price (a little over $1k) isn’t bad, but I suspect any directions I got would be german.

This paper talks about using waste vegetable oil (which I hope to be my primary fuel).

I’m going to have to filter the oil a whole lot.