I am reading Julia Boyd’s “A Village In The Third Reich”. This is non-fiction and makes a lot of use of archival information.
The book deals with the events in a specific Bavarian village as Hitler came to power, war ensued, Germany’s defeat and the aftermath.
One passage deals with the difficulties in getting relief to the village after Germany surrendered. It is written that there was no diesel, no petrol, and the trucks that were available used timber for fuel. I don’t think this is steam because mention is made of modified carburettors.
The problem was that the vehicles had to carry so much timber (or by products theref) that there was little space for actual supplies.
I have heard of steam powered vehicles, even water powered (back in the 70s - or maybe this was an urban legend), but what is described here is new to me.
My first guess was the fuel is something extracted from timber, but actually this seems unlikely given the state of devastation in Germany immediately after the war.