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The scenario: in September 1985, almost everyone abruptly disappears. Humans, domestic animals, carried/worn possessions, and vehicles currently in motion, vanish, while everything else stays as it was. (I don't know whether there is an accepted term for this kind of setting; if not, I'll use the one I just came up with, 'abruptly abandoned world'.)

A small group of protagonists have effectively become colonists, trying to reboot civilization. In the short term, they will be fine; they have access to all the infrastructure, equipment and supplies left over by the existing civilization. In the long term, they have a tough challenge of figuring out how to reproduce everything they need, before the existing inventory decays to uselessness.

One of the harder problems seems to be fuel for vehicles and equipment. Apparently both gasoline and diesel have limited shelf life, the exact figure depending on conditions and who you ask, but the consensus seems to be that even if you store them in full airtight containers with added stabilizer and away from heat, in a couple of years they will have decayed to the point where engines may fail to start.

I'm given to understand that a diesel engine can run on vegetable oil in a pinch, but vegetable oil has the same limited shelf life for the same reasons. You could produce more, but the quantity of food production that would have to be diverted to this is staggering.

Getting an oil refinery working again would be a huge challenge; those are incredibly complex machines.

It seems to me that 'make fuel from decayed fuel' should be intrinsically easier than 'make fuel from raw petroleum', and we know the latter is possible. Just how difficult would the former be? To take gasoline or diesel whose shelf life has expired, and turn it into (a smaller quantity of) usable fuel again, perhaps by somehow removing impurities? Is that possible? How difficult would it be? What, at a chemical level, is the difference between expired versus fresh fuel anyway?

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    $\begingroup$ Diesel engines will run on unmodified vegetable oil only if prewarmed on diesel fuel or kerosene. $\endgroup$
    – Zeiss Ikon
    Commented Dec 22, 2022 at 19:13
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    $\begingroup$ I would also be curious to know if there's a name for this genre of story. Would you call it a "rapture scenario" perhaps? $\endgroup$
    – workerjoe
    Commented Dec 23, 2022 at 22:06
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    $\begingroup$ We'd need to know the time frame. If it's short-term, then yes gas is a factor because with a running car your can forage a much bigger area. If it's mid-term, it's a much lower priority, as everything will run out eventually: gas, but also medicine, dentist & surgeon equipment, spare parts, lubricants. Without electricity, all power tools will fail and you're back at manual labor. (You could use rechargeable-battery power tools and use a car engine with some rigging, but these tools appears some time in the 90s, as NiMH batteries had come up.) $\endgroup$
    – toolforger
    Commented Dec 24, 2022 at 22:23
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    $\begingroup$ use kerosene, much longer shelf life, and a lot of the world still use it as a primary fuel. $\endgroup$
    – John
    Commented Dec 25, 2022 at 2:49

5 Answers 5

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The book The Knowledge: How to Rebuild Our World from Scratch by Lewis Dartnell should be a very informative read for you. It covers what one should do in your setting in great detail.

At least, in the long run, the answer to your question is to ignore fossil hydrocarbons altogether. They depend on an industry that was built up from very efficient oil sources. Those sources don't exist anymore. The same goes for coal. You'll need to go for a green reboot. Thus I present to you:

Wood/Producer Gas Car

enter image description here

Despite its industrial appearance, a wood gas car scores rather well from an ecological viewpoint when compared to other alternative fuels. Wood gasification is slightly more effiicient than wood burning, as only 25 percent of the energy content of the fuel is lost. The energy consumption of a woodmobile is around 1.5 times higher than the energy consumption of a similar car powered by gasoline (including the energy lost during the pre-heating of the system and the extra weight of the machinery). If the energy required to mine, transport and refine oil is also taken into account, however, then wood gas is at least as efficient as gasoline. And, of course, wood is a renewable fuel. Gasoline is not.

Those cards were common during the second world war. The Germans even had some woodgas tanks. Nearly a million wood-gas vehicles existed by the war's end, making this a proven technology. The image above is an amateur conversion, but this is probably what you would expect in the post-apocalypse. Professionally built woodgas cars will look like normal ones.

There are several videos on Youtube where people convert gasoline cars into woodgas cars. The process is probably not too complicated.

The big advantage is that these make you pretty independent of local infrastructure. And they look like something straight out of Mad Max. If you reboot civilization in the long run, keep in mind to plant fast-growing wood (willow or bamboo would do) for larger wood consumption.

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    $\begingroup$ And in the world the OP describes, pollution would not be a problem. Not enough people to generate the pollution. In 1985, greenhouse warming was just starting to be an issue. $\endgroup$ Commented Dec 23, 2022 at 2:01
  • $\begingroup$ Another book for my reading list. Thanks ! $\endgroup$ Commented Dec 23, 2022 at 14:59
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Ethanol.

This was one of my favorite Mythbusters episodes. An unmodified late model car ran very well on ethanol.

https://mythresults.com/moonshiner-myths

A car can run properly on moonshine instead of gasoline, without modification. CONFIRMED

The Build Team decided to test the operability, performance, and longevity of cars running on moonshine. For operability testing, they obtained three cars of the same make and model, but from different decades: 1970s (carbureted), 1990s (fuel injected), 2010s (fuel injected, modern). With 192 proof moonshine in the fuel tanks, each car was driven on a course designed to test acceleration and maneuvering. In the 1970s car, Tory struggled with the engine stalling and was unable to complete a full lap. Grant completed one lap in the 1990s car, but stopped on the second lap after his engine began to stutter and lose power. Kari, driving the 2010s car, was able to finish three laps even though she noted slower-than-normal acceleration. The 2010s car was used for the remainder of the experiments.

For the performance testing, the team tested three different strengths of moonshine: 151 proof, 170 proof, and 192 proof in a 0 to 60 mph (97 km/h) acceleration test. The car would not start on 151 proof, it averaged 19.4 seconds on 170 proof, and averaged 9.0 seconds on 192 proof (96% ethanol). Next, at Petaluma Speedway, Tory drove 3 laps running gasoline and 3 laps running 192 proof moonshine. The lap times in the moonshine-powered car were marginally better. Tory noted that even though the acceleration was slower on moonshine, the effect gave him better control on the dirt surface of the track.

For the longevity test, they went to Thunderhill Raceway Park. Grant, in a moonshine-fueled car, attempted to outrun Kari and Tori in an identical but gasoline-fueled car. Grant was able to stay ahead of them after 3 laps totaling almost 10 miles (16 km).

Pretty sweet. Any liquor store will have plenty of 195 proof grain alcohol which would be enough to fuel a car until you found a big stash of denatured alcohol. Ethanol will keep forever.

I have been trying to get brave enough to pour Everclear into the old Subaru. Maybe I will need a little for myself first.

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    $\begingroup$ I'm not sure I'd count 10 miles for "longevity". That would be more like 10000? $\endgroup$ Commented Dec 24, 2022 at 2:27
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The problem with storing hydrocarbons is that over time the atomic chains making the fuel will start interacting with each other, moving away from the rather precise composition it had initially and becoming a soup of hydrocarbon with various lengths.

The challenge is that those chains react in different ways with oxygen and do not give a clean and clear combustion, which in an internal combustion engine is bound to happen in a blimp.

Instead of making fuel out of decayed fuel, I think you can better engineer the engine. I remember that when he was explaining internal combustion engines, my professor mentioned that there were certain naval engines (2 strokes if I remember correctly) which by just changing the injection time could burn anything ("even dead sailors or engineering students", as he jokingly put it), and this was an appreciated feature in ships which could not be too picky with which fuel they could get in any harbor around the world. Additionally, such an engine that at full power runs at 60-70 rpm has more time to spare in letting the fuel burn at each cycle (and it can give some odd resonance with the heartbeat of those around it...)

If you can lay hands on such an engine, or make one which work along the same philosophy, you will much easily get a working engine.

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    $\begingroup$ @rwallace not with current environmental regulations. Earlier engines were way less picky $\endgroup$
    – L.Dutch
    Commented Dec 22, 2022 at 19:07
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    $\begingroup$ Some old tractors. Which might still be around, in collections if not in actual use. But then you get the next problems, lubricants and tires. $\endgroup$
    – o.m.
    Commented Dec 22, 2022 at 19:08
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    $\begingroup$ "Hot bulb" or "semidiesel" engines will run on almost anything combustible that can be pumped through the injectors. Ignition timing is controlled by the injection, and even the relatively small ones (several horsepower) run at fairly low rpm. $\endgroup$
    – Zeiss Ikon
    Commented Dec 22, 2022 at 19:15
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    $\begingroup$ Time stamp 1985. This was pre-stringent environmental standards, probably lots of 1970's cars around as well. Lead in gas was still a thing, it was outlawed in 1986. Fuel injection was strictly 'limited edition'. Given that I remember of smoke-belching smog machines around at that time, that ran more on oil from leaking engines ('five quarts of oil for every mile driven') than gasoline, I am sure 'stale' gas would not be a problem in clunker car engines. $\endgroup$ Commented Dec 22, 2022 at 19:41
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    $\begingroup$ Some more modern military vehicles also have these multi-fuel capability engines, since they're often less affected by environmental laws. Given that the streets are getting worse over time or are often blocked, they might be the better option anyway. $\endgroup$
    – Matthias
    Commented Dec 23, 2022 at 10:00
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Let's start with a quick Frame Challenge

It's certainly true that people will take advantage of all the benefits of their former civilization for as long as they can. But unless the disappearances are intentional, you'll be left with far too few people to run refineries... and electrical plants... and basic water systems.... You're focusing on transportation at a time when most people will be trying to figure out how to expand home gardening to produce sufficient food. Most apocalyptic stories have one basic problem: human nature. It's nice to think that we'd work together to reboot civilization, but thousands of years of history prove we simply won't do that. People who don't know how to plant gardens, purify water, and store food will act to horde and control everything they possibly can.

And whomever can control gasoline would be Tyrant #1.

Honestly, your biggest problem will be bullets. But let's get back to your question.

How do we power transportation in an abruptly abandoned world?

  • Steam
  • Horses

And you can bet that people would shift to horses very quickly. That shelf life of only a few years means people are IMO deep into survival mode. They don't have the time to fididdle around with chemistry to lengthen the time an already very limited resource can be used. You suggest "make fuel from decayed fuel," but unless your people are willing to become completely nomadic, there simply won't be enough decayed fuel around to matter. If some genius worked out how to do it without resorting to the complex refining process you've already realized can't be sustained, unless your protagonists happened to be near something like the U.S. Strategic Fuel Reserve, what was available would only last for a handful of years anyway without strict rationing.

Rats, I'm back to my Frame Challenge

Maybe you should change from the tag to . Cars decay, too. Parts for any one car become increasingly hard to find, especially if you're jury-rigging an alternative fuel source to it. Your access to anything other than steam (is there coal around? Can't depend on propane/NG, another limited resource) and horses will disappear pretty quickly without increasingly more difficult forays to secure more quantity. But, as I said, that's just a delaying action. Your people are on a ruthless clock to get a lot of manufacturing back online. With only a random 10% of the population to work with, I'm having trouble believing that.


It's really unfortunate this post is tagged .

@PaŭloEbermann points out that almost all of the horses are gone, too. I'd overlooked that aspect. It doesn't change my answer a lot — people will be using what they can as quickly as they are forced to — but it does seriously underscore how screwed the population is.

That a group of people in any one local area are left behind such that the chemistry of reclaiming decayed fuel can be worked out (chemistry/scientist), the process of reclaiming the fuel can be worked out (chemistry/engineer), the necessary facility (assuming it's not completely trivial, which it isn't or the world would have it today off-the-shelf) can be designed (structural & civil engineering), and then actually built (engineering & construction) feels mighty un- to me. And that assumes everyone is working together and playing nice rather than fighting to survive. The luxury of science is that someone else is providing the food (and everything else).

And just to add insult to injury, domestic animals are decimated, but not wild animals? So wild horses remain untouched (yay if you're in the southwestern U.S.!) but almost no domesticated horses remain — assuming horses are included in the phrase "domestic animals" (they're usually not) and not cats, dogs, and pet iguanas (what's the point of decimating cats, dogs, and pet iguanas?).

I suspect this is ending up as one of those, "give me a cool idea for my story!" brainstorming questions that won't have an actual worldbuilding foundation because rules, which must be independent of all stories, would be something like, "all the horses survive the apocalypse."

Remember, ... The vast, vast majority of apocalypse survivors are out of fuel in one month or less because most if not all of the gas stations will either (a) run out of fuel, (b) run short of electricity to drive the pumps, or (c) run short of maintenance, shutting down the software-driven pumps. If memory serves, people can't simply pop the top of the gas station tank source pipes and siphon fuel out. Folks could start siphoning the many parked cars (that didn't get decimated, like the wild horses...) but that's a time-consuming process in a (for many of the survivors) winter-is-three-months-away world.

And the number of people who have the expertise to modify vehicles to use an alternative fuel is very small, the number who can (once told how) modify the vehicles once instructed is only slightly higher.

Yeah, we're in "declare it to be so" and move on territory.

To be completely honest, I don't think there's a set of conditions that would provide the solution the OP is working for within the constraints the OP has provided.

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  • $\begingroup$ Getting horses will be difficult too, as domestic animals also disappeared. And how did you get to 10%? $\endgroup$ Commented Dec 24, 2022 at 2:31
  • $\begingroup$ @PaŭloEbermann You've got a good point about the horses, I'd overlooked the statement, "Humans, domestic animals, carried/worn possessions, and vehicles currently in motion," which means a big chunk of the vehicles are gone, too. I jumped to the conclusion of 10% based on the phrase "almost everyone." After years in marketing, people tend to think in blocks. "Many" is less than half. "half," of course, is half. "Most" is more than half. "Almost Everybody" is a lot more than half. I'm putting words in the OP's mouth, but the selected percentage will inevitably be close to 10%. $\endgroup$
    – JBH
    Commented Dec 24, 2022 at 13:17
  • $\begingroup$ I don't think that the question assumes 10%; "small group" sounds like "10-100 people" to me. (Besides, 10% would be enough to keep essentials of governments and economy running.) $\endgroup$
    – toolforger
    Commented Dec 24, 2022 at 18:22
  • $\begingroup$ @toolforger It's altogether possible the OP meant only 10-100 people, but if that's the case the question is entirely irrelevant: unless exactly the right 100 people were saved in exactly the right location, the only answer to the science-based question is, "it's impossible." I elected to assume the OP erred on the side of an answerable question, so a fair number more than 100 is required. And, no, 10% of the world population wouldn't be capable of maintaining essential government and economy when 90% of the human habitable space can't be policed. Time would be needed to reorganize. $\endgroup$
    – JBH
    Commented Dec 24, 2022 at 21:05
  • $\begingroup$ @JBH I don't think it would be possible even with the exact right 100 people ;-) - but I can't imagine that "a small group of protagonists" is 10% of the world population. $\endgroup$
    – toolforger
    Commented Dec 24, 2022 at 22:08
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When gasoline or diesel fuel is stored for a long time, chemical reactions can occur that change the makeup of the fuel. These changes can make the fuel less effective at running engines and can even cause damage over time. It's not easy to reverse these changes and make the fuel usable again, especially if it has become contaminated with water or other impurities. In a situation like the one you described, where almost everyone has disappeared and you're trying to rebuild civilization, it would be difficult to find a way to "refresh" or restore the quality of the stored fuel. Instead, it might be better to try to find a source of fresh fuel or to explore other methods of powering vehicles and equipment, such as electricity or hydrogen fuel cells.

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