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?
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.)
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.
Can you run vehicles including aircraft off diesel? Yes*
- 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.
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.
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.
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.
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.
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.