Oldschool diesel engines will happily run on B100 (100% biodiesel) but the new ones won't.

Maybe this could simply be a 'diesel engine' and we could also have a couple diesel pumps at gas stations. IRL they've got them at about half the stations you'll find in rural areas, and there's loads of farm trucks and older European cars that run off the stuff.

Granted, that would require the engine to be able to accept two types of fuel (diesel and B100) but that might not be that hard. It depends on if the engine's fuel system checks the actual id of the fuel, or the ammo_type of the fuel.