I'm developing a scavenger world set in a sort of dystopian future, and one faction has a huge monopoly on Diesel. As described as any fuel used in a compression chamber, they are able to obtain their fuel from a dried up ocean floor (which is gone due to ecological contexts). The scavengers are able to use this ambiguous fuel to power "hovering" VTOL (vertical take-off and landing) machines. Alternatively they may use turbines for lift and jets for forward motion. My question is in the title, can diesel be used effectively to produce low-altitude lift? And, alternatively, can it be adequate fuel for turbine lift?
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$\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$– L.Dutch ♦Commented Jul 5, 2022 at 3:52
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5$\begingroup$ These are two entirely different questions asked in one post. I'd recommend splitting it in two and removing the one referring to the type of fuel obtained from the ocean floor from here. $\endgroup$– NeinsteinCommented Jul 5, 2022 at 8:09
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$\begingroup$ Might also (for the sake of credibility) consider hydrate-clathrates. $\endgroup$– Escaped dental patient.Commented Jul 5, 2022 at 8:30
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$\begingroup$ Won't clathrates undergo a phase change (e.g. sublimate) at closer-to-sea level atmospheric pressure? $\endgroup$– YorikCommented Jul 5, 2022 at 17:04
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$\begingroup$ @Yorik Apparently slowly. I was hoping if a combination of sediment and the increased air pressure at the deep (ex) ocean floor might just be a feasible-sounding explanation. $\endgroup$– Escaped dental patient.Commented Jul 6, 2022 at 18:18
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7 Answers
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The difference between diesel fuel (burned in diesel engines) and kerosene (burned in turbine engines and rockets) is very subtle and can be engineered away. For example, the U.S. armed forces can use the same fuel, JP-8, to power all their aircraft (both those which can hover and those which can go really fast), all their wheeled and tracked vehicles, their stoves, their electrical generators and so on.
Long story short, the kind of diesel fuel sold in petrol stations for use in truck engines may not work too well in an aviation engine, but the kind of kerosene made for aviation engines works perfectly well in a diesel engine.
(But I don't understand how to obtain diesel fuel from a dried up ocean floor. Diesel is made from petroleum in refineries, it's not a natural substance.)
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$\begingroup$ Diesel is any fuel used in a "Diesel Engine" which is a sparkless engine that combusts air and then injects fuel to produce power. Petrol can be refined into a fuel adequate for a diesel engine, and the ocean floor is the prime source of liquid/gas fossil fuels in the modern economy; mainly due to plankton and algae beds. That's how I figured the ocean floor, all I did was take away the water. $\endgroup$– QuinnCommented Jul 4, 2022 at 23:04
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2$\begingroup$ @Quinn Are you drawing your definition from wiki? Because if you are: "Generally speaking, diesel fuel /ˈdiːzəl/, also called diesel oil, is any liquid fuel specifically designed for use in a diesel engine". Emphasis on "specifically designed for" And fossil fuels aren't "on" the ocean floor. You have to drill down. So if what you have in mind is your scavengers going down and scooping it up with a bucket, that's going to be a problem unless the goal was not to avoid drilling but to avoid underwater drilling. $\endgroup$– DKNguyenCommented Jul 5, 2022 at 0:28
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2$\begingroup$ @Quinn "petrol" is gasoline, not crude petroleum. It's already refined, and is a blend of considerably lower molecular weight substances than what you find in a fuel refined for diesel engines. And what you find underground is crude petroleum. Some fractions of it can be used for diesel fuels, but it is not "diesel fuel". $\endgroup$ Commented Jul 5, 2022 at 1:55
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2$\begingroup$ @Quinn Although some engines can run on crude oil, the oil still needs to be filtered and purified as it is full of water, sand, mud, salt and all sorts of other junk when it gets pulled out of the ground. $\endgroup$ Commented Jul 5, 2022 at 10:37
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Yes
But to start, let me address a problem: you're hanging on words (so are some of our respondents). Can diesel be a viable fuel for a hovercraft? Yes! This is because lift, in a very simple way, is nothing more than thrust vs. weight. So if you describe lightweight vehicles, diesel works just fine. How light? It doesn't matter. All you need to do for your world to be believable is declare your craft to be light enough. Say it's all made out of aluminum. Or say that many components benefit from carbon fiber scrounged from various locations. These are aesthetic details that have little to do with worldbuilding.
What you can't have is an all-steel hovercraft powered by diesel. Too heavy.
And one mistake you're making is the use of the word "turbine." You appear to want a low-altitude Harrier-style craft. That ain't gonna happen with diesel. But a hovercraft can — especially if you're using a rail locomotive-style system where the diesel engines are powering generators that produce energy that can be stored in batteries and then consumed by electric motors to drive fans.
But if you're married to the idea of having some kind of jet involved with this object, then use ramjets. Combined with diesel to create the combustive thrust, a ramjet would believably kick in once the hovercraft is up to speed, not unlike a hydrofoil boat.
And I'm voting for oil platforms
My knee-jerk reaction was to suggest bio-diesel... until you said the oceans were dried up. Bio-diesel can come from almost any living thing, but there must be a living thing. A more believable solution would be that your scavengers have taken over the ocean-based drilling platforms — which will still be there when the oceans dry up because (at least for the most part) they don't rely on the water to stay "afloat" or standing.
They may, and probably do, rely on the water to cool equipment, promote drilling, and who knows how many other things, but why bother with that level of detail? Scavengers taking over platforms that stand hundreds of feet above the ocean floor to continue the oil-pumping process in a decidedly Mad Max kind of way, leading to islands of tribal control, is simply too cool to pass up. Please don't get fixated on making your world "too real."
There are more than 12,000 oil platforms in use today, and it's beyond believable that as many of them as you want can be used to continue producing diesel — and it wouldn't be that hard to scavenge refinery parts from what used to be the mainland (there are thousands of refineries world-wide) and haul them out to the Oblivion style oil platform outposts to make self-sustaining diesel producers.
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$\begingroup$ Oh boy, a useful argument. So a major problem I have is that the vehicles they're using are HEAVY. I'm talking several tons of tungsten. I did indeed also have trouble looking for the right type of engine, I meant to describe those fans that are inside a circular case as is the case with a jet engine but without a fiery output. I think you know what I'm describing. You said they're probably storing power in batteries; does that mean they're burning it beforehand or during flight? Correct me. Oblivion? What do you mean, Todd Howard or Tom Cruise? $\endgroup$– QuinnCommented Jul 5, 2022 at 0:58
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$\begingroup$ As for the drilling, the oceans dried up LONG before humanity showed up in this area; these scavengers have been setting up original drilling operations in what are now open oil fields. They aren't Derricks, so to speak, they're pumpjacks. The Derricks are present indeed, but in the other side of the world where the oceans turned into glaciers and you can walk onto the Derrick from the tundra; there's an entire city on one, but it's a relatively new creation, about two hundred years old or so. $\endgroup$– QuinnCommented Jul 5, 2022 at 1:05
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$\begingroup$ "Oblivion" = Tom Cruise. Rail locomotives use diesel engines to charge batteries. The batteries are used to drive electric motors, which are what actually move the engines. The value in this is that down-hill the electric motors become electric brakes (aka generators) that also charge the batteries. This makes the locomotives more efficient. In your case, the electric motors would draw from the batteries when lifting and charge the batteries when descending. You have a problem with heavy. None of this works with heavy - other than wheels. $\endgroup$– JBHCommented Jul 5, 2022 at 4:19
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$\begingroup$ I think you may be confusing engine types. Turbine engines are by far the best power to weight ratio, much better than series diesel electric, and they run just fine on diesel fuel - for example, the M1 tank. If you are looking for light weight, turbine engines are the only way to go (that's why planes and helicopters use them) $\endgroup$ Commented Jul 6, 2022 at 3:48
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Can you run vehicles including aircraft off diesel? Yes*
Depends on:
- What is being defined as diesel? Or are you using diesel-1, diesel-2, jet-a, what ever comes of the 300 deg C tap of the refiner etc.
- What is your engine designed to use. Engines can be designed to use almost any petrochemical others could be optimized for very specific fuel such as 99.99% pure kerosene.
- How pure can you make the fuel, increasing purity is increasingly expensive to refine/produce. Fuel of very specific composition and engines designed for that specific composition can have better performance, less maintenance, and other tradeoffs.
Finding diesel.
Typical oil sources do have ocean origin stories. however its crude oil that will be found, not refined products. To the same degree miners don't mine steel ingots.
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$\begingroup$ They obtain the crude oil and refine it, I thought that was a given. $\endgroup$– QuinnCommented Jul 5, 2022 at 0:51
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$\begingroup$ @Quinn in that case, why are they producing diesel fuel when what they need is jet fuel? $\endgroup$ Commented Jul 5, 2022 at 1:57
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$\begingroup$ Plenty of historical planes used diesel $\endgroup$– QuinnCommented Jul 5, 2022 at 2:07
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1$\begingroup$ @Quinn Because diesel is what they had. Like diesel engines, gas turbines can run on a wide variety of fuels, including gasoline, diesel, marine diesel, natural gas, and a mix of cryogenic liquid hydrogen and liquid oxygen, and some are specifically built to accept a wide range of fuels, or fuels that are more available. However, a hydrocarbon fuel blended specifically for use in high-performance jet engines will not be identical to one blended for diesel engines. But they're making refined fuels from crude petroleum, so why would they make diesel if they're fueling jet engines? $\endgroup$ Commented Jul 5, 2022 at 11:36
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1$\begingroup$ @quinn question states "type of diesel would you mine", "able to obtain their fuel from a dried up ocean" I read that as expecting the ability to directly extract diesel without refining, Because if there is a refinery, it can tuned to produce practically any hydrocarbon based fuel(s) desired.. $\endgroup$ Commented Jul 6, 2022 at 0:36
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If plankton and algae are the source of the fossil fuel, they will need to be buried for millions of years for the conversion to take place That their location used to be an ocean floor will be irrelevant.
And what they will have turned into will be raw petroleum. Yes, diesel can be extracted from it, but in the process, so can gasoline, kerosene, methane, propane, etc.
If you are working with recently deposited plants, then fermentation and distillation into alcohol sounds a lot more practical as a source of liquid fuel.
answered Jul 4, 2022 at 23:30
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1$\begingroup$ Plates also move slower than oil takes to form, there remains more oil under the ocean than there is on land today. (When I say on I mean under). The fact it's a dried ocean floor means all that marine fossil fuel is easily accessible. Recently deposited plants isn't necessarily an option, either; that ocean had been dry for quite some time. $\endgroup$– QuinnCommented Jul 5, 2022 at 0:49
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$\begingroup$ @Quinn, the only way it will convert to petroleum is if it is buried for a very long time, without any exposure to air. $\endgroup$ Commented Jul 5, 2022 at 1:01
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$\begingroup$ I don't see how that's a problem; it was buried for a long time, even before the ocean dried up. Oil doesn't just vanish over time. It's all still VERY underground. $\endgroup$– QuinnCommented Jul 5, 2022 at 1:07
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Look into https://en.wikipedia.org/wiki/Ground-effect_vehicle Maybe it's not totally same thing as you want, but it's pretty interesting technology that can be used not only above water.
If we speaking about VTOL: refined fuel can be different quality. It depends on two things - fraction of light weight atoms (which easier connect to O2 atoms) and presence of dirt (which can be heavy weight atoms or heavy metals). Main problem is not to produce lightest and highly octane fuel, which still be pretty much expensive. But to produce really clear fuel. The bigger force you need - the bigger temperature must be reached. With temperature of burning fuel in jet engines and bad fuel - all the insides of jet engine will quickly become clogged with a layer of petrified plaque from heavy fuel fractions. Which will inevitably lead to damage.
Generally speaking. You can't use diesel in jet engine, because it's to dirt.
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1$\begingroup$ As it’s currently written, your answer is unclear. Please edit to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers in the help center. $\endgroup$– Community BotCommented Jul 5, 2022 at 9:52
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Gas turbine (Brayton Cycle) engines can run on just about any fuel you can imagine. In real life we regularly run them on natural gas (power plants), diesel (M1 tanks), jet fuel (planes and helicopters), and heavy oil (frigates and destroyers). You don't even necessarily have to design the engine for each fuel, only the fuel delivery system. M1 Abrams tanks (which use a 1500 HP turbine engine) can burn any fuel they can be supplied with, a fact the army uses to it's logistical advantage.
Bonus for your hovering machines - they also give the best power to weight ratio, making them a really good option for your application.
Compared to a diesel cycle engine, turbine engines can be finicky and inefficient, but there's a reason that every application where weight is a primary consideration uses them.
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Judging from the answers I read it seems that something is not clear. Even though the process to turn dead organic matter into oil usually takes ages[*] it could be very fast. For example, if you put sewage sludge with some water in an autoclave with processes like pyrolysis or hydrothermal carbonization you can produce fuel oil quite quickly even though it would be full of polluting substances. In the case of the OP what oil could they get? Organic matter trapped under sediment near the tectonic ridges full of volcanoes could be turned into oil quite quickly with the help of geothermal heat. If the sediment layer is not thick enough to create pressure it could still block oxygen and near a volcano the organic matter could be turned into something similar to tar which could be liquefied.
It would be different from the kerosene we use today in aviation, but what matters is that it will have less energy density. If the engines and the hovering machines are well designed with lightweight materials and exploit the ground effect they can still fly, only the range would be limited.
The only difference from the OP is that I would add vegetable oil to the fuel. Even if the imagined world is a wasteland some hardy plants must be able to grow otherwise it would be uninhabitable for men.
[*] Note: oil takes thousands of years to form because organic matters sinks slowly underground under the sediments that build up slowly. Furthermore not everywhere underground you have a lot of geothermal heat. However if you have enough heat and pressure the aforementioned thousands of years are not needed.
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$\begingroup$ I mean I still don't see why time is an issue, oil takes millions of years to form, and plates take millions of years to move, most ocean oil is from when those parts were still ocean. Geothermal vents ARE however a very important topic I didn't address/think I needed to mention. The thin oceanic plates would have heavy volcanic activity by default, especially considering there's some very heavy tidal forces going on in this setting. $\endgroup$– QuinnCommented Jul 7, 2022 at 7:39
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$\begingroup$ "I mean I still don't see why time is an issue," Quite the opposite. I meant that if you have heat and pressure you don't have to wait millions of years. So, the settings in the question is possible. Since the oceans are evaporated you would miss the pressure, but dead algae piling up over the heat of a volcano and isolated from oxygen by little sand could provide the fuel you need. $\endgroup$ Commented Jul 7, 2022 at 16:30
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$\begingroup$ BTW. I never talked about Geothermal vents, they have nothing to do with my answer. What I took into account is only geothermal heat. That should be enough to cook the organic matter. $\endgroup$ Commented Jul 7, 2022 at 16:52