Booze.
Use E25 (75% gasoline - 25% alcohol). Even if fuel consumption is a mite higher, 20% savings on gasoline.
A range of modifications to the basic Diesel cycle would permit use of much less critical fuel and substantially lighter engine construction at the cost of some reduction in thermal efficiency. These range from the the early Hesselmann engine (a direct injection multi-fuel spark ignited engine) thru a range of precombustion Diesels, employing L'Orange and, later, Ricardo Comet chambers, fitted with glo plug or sparkplug igniters. The injectors would be much more robust and less critical than those necessary for pure Diesels and Cetane rating control would be unnecessary.
3 - uses a different part of oil refinement outcome than gasoline - pro
Hence, diesel can be used alongside gasoline, cannot replace it
Wood-fired tanks?
You might also substitute wood shavings or "wood oil" (a liquid derived from it; what it's correctly called, I don't recall ), both produced by pulp &/or paper plants. There's also industrial methanol, tho IIRC, that requires petroleum to produce...If water supply could be relied on, reciprocating steam (including as much condensing as practical) would be my choice despite its relatively low efficiency, since powdered coal (delivered by stoker screw to a high pressure blower and the burner in the flashtube boiler) would eliminate any petroleum requirement.
That's going to obstruct field of fire over the rear deck, y'know...
I was gonna roll with .. horses.. lots of horsesWood-fired tanks?
If you're willing to go further afield than even steam, there's the Stirling engine , which can also use powdered coal, wood chips, low grade petroleum (including bunker), or wood (like a fireplace...), with the added benefit of being shiny & new, appealing to Hitler's passion for anything never done before.
Horses was my first thought too, but I went with wood because I thought it would be cooler.I was gonna roll with .. horses.. lots of horses
but wood fire would be cool as well.
Honestly any mechanized military is going to need petrol. the best way to relieve the dependence is to become independent of it, which is an oxymoron if you want a modern military.
so to that end. spend less on gas guzzlers and heavy equipment that will consume more oil/petrol. secure oil production, make friends, good friends with oil. Don't decide to go fight wars and take over the world without a high limit gas station credit card
If oil is a major weakness for Germany, then simplifying vehicle production so you can have more tanks just makes the problem worse. Getting rid of tanks .... Well, you can't. Relying on horses... They already do. I think they're stuck. Whatever efficiencies you can play around with in engine design will at best only affect new manufacturing, introduce a whole host of new logistics and maintenance problems to do with servicing yet more types of engines in the field, and even then will only be shaving off consumption around the margins.Have somebody high up in the German power structure do the math and find out that in the event of a war oil would be a major weakness for Germany.
Research is put into getting engines to be more efficient, little if any research was done on that in the 1930s.