A fiend who I played 1st edition with has finally made it back to Australia from Europe. He is a chemical engineer and a great fan of Twilight (I ordered a box set for him).
We were talking about the new rules and the issue of fuel came up.
Firstly it is nearly impossible to run a diesel engine on alcohol: it has poor self-ignition qualities and would dramatically limit the power output. The only way around this issue is to use multiple fuel injectors which is a change you can't retrofit onto existing engines.
Petrol engines also struggle to run on 100% alcohol.
But all isn't lost.
Europe has a long history with coal hydration - making an oil substitute from coal. Such plants would be primary targets during WW3 but you could set up limited production in underground locations. Oil produced from coal hydration is low octane and no suitable to high-performance tasks like aero engines.
Diesels will run on a surprisingly wide range of oils - I have put old cooking oil into my Landcruiser and it runs fine - and is the best engine for WW3. A range of plants can be used for oil, although this has the issue of taking possible food sources and using it for energy production.
Another interesting fuel source is old plastic. Plastic can be broken down into a form of hydrocarbon that can be used to produce fuel.
You then have gas - Liquid Petroleum Gas and methane. Methane can be generated from waste and can be used to run stationary generators (think Barter Town in Mad Max 3).
There is also wood gas which was used to power vehicles in WW2 and is still used by survivalists today, but it is bulky and vulnerable (plus you have a fire attached to your vehicle) and low powered, but you could see civilian vehicles running on wood gas.
What all this means however is that military vehicles are likely to be running on a blend of fuels gathered from whatever is available. So a jerry can may have a mixture of actual petrol or diesel along with ethanol, plant oils, old plastic and anything else that will burn in an engine. You would have different blends for petrol or diesel, but for game purposes could have a blend that works for both.
In fact older engines are better in such circumstances with a higher tolerance to bad fuel, which would advantage military vehicles over civilian and older vehicles over newer. Gas turbine vehicles will be really tricky to run with ersatz fuels.
Settlements may be generating methane to run generators or boilers. Areas still under government control may be collecting gas from coal fields, hydrating for oil on a small scale, as well as burning the coal itself. Civilian vehicles may be running on wood gas.
None of this is necessary in game terms but it is interesting to see just how things could work after a nuclear war.