Yeah, there’s a lot of stuff out there, including the GEET engine that can run on waste oil, paint thinner, diesel, crude oil etc, but it’s pretty clunky and involves water, so winter operation would be a provlem...but I’ve seen it work.
The “producer gas” generator is also interesting, it would work well in a pickup or vehicle with a trailer to haul the wood fuel.
Running a diesel car on deep fryer oil looks the easiest. You might want to mix it with a little alcohol or something to thin it.
Since we made it through Biden and the RATs, I’m not too worried about an oil crisis.
The producer gas things used to be on the running boards of the old cars during WWII. Some of the old movies even had them.