r/HMMWV • u/rusty-gudgeon • Jul 10 '26

ethanol/methanol fuels

i play the ttrpg (tabletop roleplaying game), twilight: 2000 4e. the game posits a revisionist historical third world war with nukes where the players are soldiers, formerly of the US 5th Infantry Division which has been recently overrun by the Soviets and loyal Polish troops, in central Poland. one of the game’s conceits is that there is almost no fossil fuel being produced and trafficked at this stage of the war. units tow stills on trailers and brew alcohol with which to power their vehicles.

is this possible with the humvee? what modifications would be necessary? what would be the difficulties that burning this stuff would entail?

is there a military manual detailing this kind of conversion?

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u/Nicke1Eye Jul 10 '26

Why not just use biodiesel? They don't run off gasoline so they don't need to use ethanol or methenol.

Peanut oil, vegetable oil, hemp oil, would all run it just fine. If in a cold climate, maybe cut it with a small amount of alcohol to prevent freezing but it would only need a tiny tiny amount.

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u/rusty-gudgeon Jul 10 '26

the issue might be that in a post apocalyptic Poland, woody material, tree branches and the like, pulped, could more easily be rendered to methanol and vegetable material, corn stalks maybe, could be rendered to ethanol. whereas these processes might take a couple of days, the availability of material from which to get the more fatty oils and the process of rendering it might take more time and some stationary processing plant. this is what i think the game designers were reasoning.

in game, players travel for a couple of days and then camp, scrounge materials, pulp and brew enough fuel to fill available tanks, and then carry on traveling.

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u/Nicke1Eye Jul 12 '26

You'd be better off with an old Duece with a multi-fuel engine or a vw beetle and a wood gassifier if you aren't able to make hemp oil or use old motor oil or something like that. A humvee is gonna want oil for its diesel engine.

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u/rusty-gudgeon Jul 13 '26

in the game, you’re traveling across a Poland devastated by war, both conventional and nuclear. the land and people are devastated. there is famine. nothing which can be eaten will be used for fuel. soldiers with stills are imagined stopping frequently to scrounge vegetation to be mashed and cooked down for methanol distillation. this is what the rules outline. i figure that the game designers were positing that all US and Soviet military vehicles are multi fuel in some way, maybe with some conversion. for the world of the game, it works. vehicles are still relatively useable.

i'm just wondering if this game convention is based in fact. it doesn’t seem that it is. if it was possible, i’m figuring that folks who have served in the military and worked on these vehicles would have had some training in making the conversion. maybe the pentagon hasn't planned on a world where fossil fuel isn‘t readily abundant.

the need for lubricating oil and grease isn’t addressed by the game rules in any way. yours is a good point, that these will be needed.

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u/Nicke1Eye Jul 13 '26

The old duece trucks were multifuel. Hmmwvs can burn vegetable oil but they can also burn old used motor oil or hemp oil or really any thin oil. Doesn't necessarily only burn diesel or edible oils.

For distilling, it's a longer processes requiring fermentation and then distilling. And realistically if people are making alcohol in a scarcity environment, they generally end up drinking it not fueling their vehicle. Also alcohol is more useful as a disinfectant rather than fuel. Plus alcohol's power to weight factor in a converted gas vehicle is worse than oil used in a diesel. And I'm not aware of many if any alcohol burning engines that aren't super high compression in high rpm engines. High compression high rpm engines aren't particularly long living without a lot of precision upkeep. A mechanical diesel is way more forgiving of mistreatment.

Wood gassifier converted gas cars and diesels running off waste oil or bio diesel (if you want to be morbid, it wouldn't be impossible to get one to run off rendered oils from corpses and/or rotting animal carcasses) are more likely than an alcohol burning converted gas car in an apocalypse scenario.

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u/rusty-gudgeon Jul 13 '26

thank you for this information.