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Typically, gasoline has a short shelf life (some months, maybe a year). This is handwaved in some post-apocalyptic settings where the writer wanted vehicles to play a major role (such as Mad Max — unless there was an explanation that I don't recall).

I would like to create a similar setting, but without having to handwave that detail. Are there plausible ways for modern-day passenger vehicles to remain operational in such a setting?

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    $\begingroup$ Is ethanol not an option ? $\endgroup$ – ksjohn Aug 31 '17 at 15:50
  • $\begingroup$ @ksjohn It could be. If you add an explanation about how it can be manufactured in a post-apocalyptic world, it would be a very useful answer. $\endgroup$ – Sigma Ori Aug 31 '17 at 16:06
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    $\begingroup$ Making ethanol in a post-apocalyptic world would be entirely achievable - effective distillation was being practised in the middle ages and modern 'moonshiners' would be more than capable of making ethanol to power cars. $\endgroup$ – Matt Bowyer Aug 31 '17 at 16:36
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    $\begingroup$ @MattBowyer, as early as 10 years ago, I'd quibble about having to mod the engines of cars to survive running on ethanol but more and more cars are being made "flex fuel" now days that if the big bad happens 10 years from now, it would probably be rare to find a car that won't run on it. If they're not all electric by then. $\endgroup$ – ShadoCat Aug 31 '17 at 17:17
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    $\begingroup$ Have everyone use diesels, they run with used deep frying oil.... $\endgroup$ – PlasmaHH Sep 1 '17 at 8:08

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Modern gasoline has a shelf life problem because it contains ethanol, which, over time, absorbs water. If expired fuel is in a container, it is relatively easy to separate ethanol/water phase from "real gasoline" (hydrocarbons) and use it. If expired fuel is already in the tank, the task gets more tricky, but still doable by low-tech methods.

remove water from gasoline

P.S. There was probably no E10 fuel yet in 1970/80s Australia, so gasoline was eternal :)

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    $\begingroup$ 100% Gasoline was never eternal, but if stored in sealed, temperature controlled environment it was good for a number of years. Cars left on the road after the fall would not qualify as proper long-term storage. $\endgroup$ – Gary Walker Aug 31 '17 at 18:35
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    $\begingroup$ Personal experience: during the Arab Oil Embargo, I would drain gas from the tanks of vehicles that had been sitting in the farm junkyard for years, maybe decades. Never had problems, though admittedly this was before electronic emissions controls. $\endgroup$ – jamesqf Aug 31 '17 at 18:55
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    $\begingroup$ Petrol/gas like many things doesn't really expire, it just degrades a bit. Decades-old petrol should be fine, especially in a basic engine that is tolerant of poorer-quality fuel. $\endgroup$ – Matt Bowyer Aug 31 '17 at 20:42
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    $\begingroup$ @GaryWalker Gasoline in a full (= no air) container is good forever, because there is no reasonable mechanism by which it could foul. And you can also forget temperature control, as long as it's not so hot the seal in the container lid fails. And if it was in the tank, and the car was not parked in a desert, you strip the water, and it will still be totally OK after a decade or two. $\endgroup$ – Karl Aug 31 '17 at 20:46
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    $\begingroup$ Any fuel tank that is not sealed will draw water over time, E10 or not. Diesel oil tanks on boats are notorious for it. Of course it's slightly worse with E10, but much more with half-filled tanks. Every time the outside temperature drops, small drops of condensed water sink below the fuel surface, and never come out again. $\endgroup$ – Karl Aug 31 '17 at 20:52
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You can turn coal into oil; process is called liquefaction.

It is not currently economically useful, but it's not very complex and any steampunk technology can do it.

Note here still are many open-sky or otherwise not very deep coal mines that would be accessible to post-apocalyptic setting (not to mention coal can be manufactured from wood), where oil is much more difficult to reach.

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    $\begingroup$ You can't make coal from wood (although if you have a few million years you can wait for it to happen). You can make charcoal, but that's not much use for making oil. You can however turn wood into ethanol. $\endgroup$ – Matt Bowyer Aug 31 '17 at 20:43
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    $\begingroup$ You can also turn wood into syngas. Wood gasification is also available to any steampunk or dieselpunk-style technology, and plenty of engines will run on it. $\endgroup$ – Logan R. Kearsley Aug 31 '17 at 20:58
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    $\begingroup$ @MattBowyer Gasoline (~alkanes) can be synthesised (Fischer-Tropsch process) from carbon monoxide (syngas, more exactly), and it doesn't give a damn if it was coal or charcoal before. $\endgroup$ – Karl Aug 31 '17 at 21:05
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Several alternatives have been offered, including coal liquefaction, brewing your own ethanol, stripping water from old hydrocarbon fuels and so on. One alternative which hasn't been mentioned yet is "wood gas".

This was done during the Second World War when gasoline was being rationed, and used a process called pyrolysis to burn wood or charcoal in a low oxygen environment inside a "wood gas generator". The gasses emitted from the process were full of combustable products including Hydrogen, Carbon Monoxide and various aromantic hydrocarbons in low concentrations. This was fairly inefficient and low energy fuel, but with some adjustments 1930-40 era engines were able to use this.

A wide variety of different gassifier designs can be found here. The FEMA design is deliberately simplified so use in a post apocalyptic environment can be assured since it needs no expensive or hard to create parts, but can produce a lot of tars which gum up the engine. The Imbert designs is the classic WWII era one, while the Keith gassifier is considered the gold standard today.

enter image description here

wood gas generator attached to car

I advise anyone to carefully study the system before building your own, since Carbon Monoxide is one of the products of this process, and is very deadly. Don't play around if you are not sure what you are doing.

Cross section of a modified Keith gassifier.

enter image description here

The air enters at the bottom in blue, warms up as it flows through the heat exchanger, and warms further flowing past the warm gasifier itself. This preheated air adds substantial energy to the combustion, increasing the efficiency. Also notice the dual pipes exiting the gasifier; these are 3" pipes. They go into the settling chamber, expanding and slowing down. This causes them to release some of their energy to the heat exchanger, and some of the dust settles out. Gas exits near the top of this chamber, again in two 3" pipes, right into the cooling rack.

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Maybe Gastown was natural gas. Or biogas! I see gas powered vehicles going around town all the time now. Lots of buses.

Biogasbuss

Biogas fermenter

Your postapocalyptics can use a fermenter to generate their own biogas out of mutant corpses, wilted flowers and their own bodily secretions. You might want some barbed wire on the sides of the Biogasbuss to make it properly MadMaxy. Also cover up that "grenare värld" heart with some skulls or something.

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    $\begingroup$ When i looked at that first picture, i read it as "BIGASSBUS". Associative reading at its finest... $\endgroup$ – katzenhut Sep 1 '17 at 14:29
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Steam transport allows to burn anything. This is the reason why Russia still has steam locomotives that are conserved and waiting for the apocalyptic times when oil will not be easily accessible. During the great depression in the USA people burned grain in locomotives.

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Fuel has a shelf life

Different fuels last different lengths of time depending on different storage characteristics. But, in the end, no petroleum-based fuel lasts forever in common real-world storage environments.

Biofuels and other alternatives to gasoline/petrol

Dump gasoline/petrol based cars. Those fuels, especially with today's use of ethanol-additives, won't hold up. Stick to diesel engines. Vegetable oils, animal fat, etc., can be burned in these engines. Sure, it's hard on them, fuel economy goes down, etc. but the engines can run, which is far easier to generate locally than any other modern engine fuel.

Bigger problems exist

Even if you solve your gas problem, you have bigger worries. If you have modern engines, then you have to worry about parts that wear out, sensors that fail, electronics, batteries, rubber and plastic parts that degrade over time, belts, etc. For all practical purposes, none of these parts can be fabricated in your post-apocalypse world.

So your engine has a shelf-life. As do your tires, your fuel lines, your...

Yes, you can restore older engines to life with much care and feeding on the mechanics' part. But that still depends on scarce resources: parts, skilled labor, patience, and spare time.

Focus long term

Use the engines you can get for as long as you can, but don't get attached.

Instead, as soon as your world is stable enough to survive day-to-day on, begin working to decouple your survival from modern vehicles. Clear roads and bridges, dig your pits etc. with the construction machinery while it works. But assume that within the next 5 to 20 years, you will hit a wall where any given vehicle will fail beyond repair for some reason or other. Maybe because you can't scavenge a spark plug that fits. Or that rubber fuel line dry rots. Whatever. But you can't go back to the store and buy a new one.

So focus on phasing out the vehicles so they aren't required for survival. Start learning to breed and ride horses, for example.

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    $\begingroup$ Great answer on looking forward, wish I could upvote twice. Did you ever read Robert Adams "Horseclans" Novels? They did exactly this. Used tech while they could, learned to make yurts and switched to a nomadic lifestyle a'la the Mongolians. They author made a point of old tech just plain wearing out and moving on before that point for a safer transition $\endgroup$ – Paul TIKI Sep 1 '17 at 16:44
  • $\begingroup$ @PaulTIKI No, I haven't read them. But I might have to! I love post-apocalypse as a genre, even though I get tired of some of the less-believable tropes. $\endgroup$ – CaM Sep 1 '17 at 16:45
  • $\begingroup$ They may be hard to find. They have some fantasy elements, like telepathy with horses (a side effect of radiation from the nuclear exchange) and the founder of the Horseclans being effectively immortal (no reason really given, but He's the one that brings several folks together and starts welding them into a successful survival group), but it works as a whole. Most of the stories are set North America, a few hundred years after the big nuclear exchange. One or two are set just after the war. $\endgroup$ – Paul TIKI Sep 1 '17 at 16:50
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You can convert a lightweight internal combustion engine to steam, it is even easier with 2 cycle engines. You have to cut and weld the cylinders and making a new crankcase improves the efficiency a lot, but a decent mechanic could do it. Some engines (tall double acting cylinders) work better than others of course. You don't get the same power you do with petroleum fuels, but it will run around just fine. You can still get high speed you just do not accelerate as fast.

People have even converted trucks to run on firewood. And of course a mechanic with some fabrication skill could just make a steam engine. As a bonus if you design them right steam engines can be used to purify water as well, always a bonus in a post apocalyptic setting.

Also consider a liquid burning steam engine will burn expired fuels just fine.

Alternatively you can re-refine expired gasoline into usable gas, it's not to mechanically difficult. It will run out eventually but this will extend the time you can use unaltered cars.

Finally many vehicles are made to run on kerosene which is both easier to refine and has a far longer shelf life. Propane is even better with an unlimited shelf life. Besides existing engines that run on it converting a gasoline car to run of these is not that hard.

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  • $\begingroup$ Old two cycle diesel engines can be modified as "inflow" steam engines by reversing the flow so steam is injected through the exhaust valves and exits though the intake ports cut in the cylinder sides: internationalsteam.co.uk/trains/newsteam/modern11.htm $\endgroup$ – Thucydides Sep 1 '17 at 22:23
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Lets go to Barter town! Barter town has methane! Barter Town has Pigs!

Pigs poop and methane cometh form pig-s#$t.

Ok, what is my point here? The internal Combustion engine, in theory, runs on a fuel being aerosolized, mixed with air, then detonated in a sealed chamber to generate lateral movement which is then turned into rotational movement which then, through a series of gears to produce work....That means that with a variety of fuels you can do this. It doesn't have to be petroleum based. In fact, there is a very wide range of options, including methane derived from pig-s#$t.

though if you chose that, you'd have to sing a top 40 hit while wearing a chain mail dress.

Anyway, what it really comes down to is how much work do you want your characters to have to do?

Biofuels are relatively easy, if not high yield. Diesel engines, according to legend, were built in the first place to run on peanut oil. Anyone who has abused themselves with flaming drinks knows about ethanol. You just have to remember that if you are using food crops for things other than just food, you have to hold back enough so you won't starve.

Wood Gassifiers are good. So is plain old steam.

Here is what you can do.

1) Pick an alternative fuel...any fuel.

2) Google "downside of ...."

3) bingo, you now have a pretty good idea of how much work your characters will have to do.

If you do it right, you get realism and some very good plot devices all in one shot.

Who runs Barter Town?

The lady singing a top 40 song while wearing the chain mail dress

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What is preventing the brightest of the post-apocalyptic population from banding together and frugally using what yet-to-expire gasoline they have locally to journey to known petroleum repositories within their calculated travel distance and refining it---and the collected old gasoline---on demand? What has the proposed apocalypse wiped out? I mean my distant relatives made their own acetylene. How hard could it be to learn in a survival situation?

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    $\begingroup$ "Natural oil" isn't gasoline. You can't use it in an engine without some rather complex refinement. $\endgroup$ – duskwuff Sep 1 '17 at 7:00
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    $\begingroup$ it would be far easier to collect bad gasoline and refine it into usable gas. $\endgroup$ – John Sep 1 '17 at 13:27
  • $\begingroup$ @duskwuff, true. $\endgroup$ – user42036 Sep 1 '17 at 17:02
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Post apocalyptic world we will naturally discover that the most abundant element on earth, hydrogen, H2 can be generated at the point of use from water using not electrolysis but harmonic frequencies, spontaneously releasing vast amounts of energy. to put this another way

"If energy fails, life fails so when the sun burns out it's lights our"

Now that is an apocalypse.

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  • $\begingroup$ Hi John! Welcome to worldbuilding stackexchange! The question asks for a plausible ways for modern-day passenger vehicles to remain operational in such a setting, not "alternative fuel for use". In my personal opinion, you can't just pour hydrogen into your fuel tank and expect it to work just like gasoline. Perhaps you could revise your answer to properly answer the question. $\endgroup$ – Hendrik Lie Sep 2 '17 at 6:03
  • $\begingroup$ Can you give a pointer to process? AFAIK O2 + 2 x H2 have much more energy than 2 x H2O; if you want to break down water you need to give it the "missing" energy, in some way. I would be interested in which "harmonic frequencies" can help in the process. $\endgroup$ – ZioByte Sep 2 '17 at 7:03

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