this post was submitted on 13 Mar 2025
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Why hasn't anyone tried making a combustion engine using fusion? (lemmy.ml)
submitted 6 days ago* (last edited 6 days ago) by doomsdayrs@lemmy.ml to c/asklemmy@lemmy.ml
19 comments fedilink hide all child comments
 

I searched for the engine briefly, and found no mention of anyone thinking of this.

This post comes from this comment of mine.

In my original comment, I note that I immediately think the strain would blow the entire thing a part.

What are your reasons of why you think would not work, or why no one has tried, or maybe you know someone who did try?

Note, Not the size of a car. More like the size of a cargo ships diesel engine. ("Wärtsilä-Sulzer RTA96-C" as an example)

Imagined design. Original Post

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[–] bjoern_tantau@swg-empire.de 23 points 6 days ago* (last edited 6 days ago) (1 children)

Uhm, we haven't even managed to make fusion produce net energy with a large reactor. What makes you think that we could do it on the scale of a car?

Edit: Now I read your comment. It doesn't matter where the pressure comes from. The hard part is sustaining and controlling the fusion in a way that we can extract more energy from it than we put in.

[–] doomsdayrs@lemmy.ml 4 points 6 days ago* (last edited 6 days ago) (1 children)

I don't imagine it being the size of a car?

I imagine it being a huge facility, with a steam generator attached utilizing the coolant heat and more.

The pistons would be similar in size to the pistons of a diesel ship.

Take the "Wärtsilä-Sulzer RTA96-C" as example.

[–] MrVilliam@lemm.ee 7 points 6 days ago (1 children)

So you mean more like a power plant? Are you thinking like brayton cycle, rankine cycle, or both (combined cycle)?

I don't know much about fusion, but a big part of how a brayton works at that scale is air. For a jet engine the combustion expands, spinning the turbine or afterwards, and this spins the axially connected compressor section which sucks and squeezes air prior to the combustion chamber. A piston engine would be less continuous, so might be better suited? But in any case, this relies on whether fusion moves a shitload of air like a combustion engine does, (and like I said idk if it does,) and if it does then I guess it could be possible so long as pressures and temperatures stayed within metallurgical limits. I also don't know how economical it could be, but let's pretend that this is entirely exploratory and costs don't matter. I'm not gonna shit on your idea because the truth is that I don't know and you could be predicting a breakthrough idea 100 or 50 or 20 years ahead. Is fusion something that can quickly explode like in a piston engine in the first place or would it be better to run continuously through a turbine? Is that even possible? Idk.

Regarding the rankine cycle, that's the assumed application of fusion power. It's just the newest, best idea for how to boil water to superheated steam to spin turbines and condense back to feedwater. I only even bring this up because you specifically mentioned a steam generator, and that really only makes sense if you're utilizing the rankine cycle. Combined cycle would be using that piston/turbine engine thing from earlier but recycle the exhaust heat to a HRSG which loops to a steam turbine and condenser and back. But you need a large volume of fairly continuous hot exhaust flow for this, so it's wholly dependent on that thing I said I don't know lol.

We need some input from people who know something about fusion. I don't really know how we would control fusion while throwing a shitload of air into it and getting an even bigger shitload of air out the other end. Without that input, idk how anything other than rankine could be managed.

[–] doomsdayrs@lemmy.ml 1 points 6 days ago* (last edited 6 days ago) (1 children)

Thank you for entertaining my thoughts.

I tried to draw what I am imagining.

Does this help you see what I am thinking of?

[–] MrVilliam@lemm.ee 2 points 6 days ago (1 children)

I don't know of any piston that can initiate a fusion reaction, but that doesn't mean it's never going to be possible. But I think that such a thing would take teams of top researchers decades to figure out with any sort of reliability.

Regarding the rankine cycle, the diagram would need to be much more detailed. From what I am understanding of your diagram, no it couldn't work that way. I don't know a lot about fusion, but from my experience in fission nuclear power plants and combined cycle natural gas plants, I can make some assumptions about what to expect from a rankine cycle plant regardless of fuel source. You would need to ensure that only superheated (dry) steam is ever touching the steam turbine blades, and there is a ton of essential equipment that does exactly that. There are a ton of resources out there to learn more about this, and I'd recommend searching "rankine cycle explained" on YouTube to get started. General overview stuff might touch on things like drums and reheaters and condensers and vacuum pumps, but every little piece like that could use its own deep dive, really. It's fascinating stuff.

Overall, I think there is already a general understanding of how to make a fusion rankine cycle power plant work, and it's now just a matter of getting a sustainable reaction and then finding the optimal design and operation to safely and reliably maximize the extraction of that thermal energy to perform work. Should this be more like a BWR or a PWR plant? What do refuel outages look like? What sort of preventive maintenance will be required? What sort of hazards will workers be exposed to, and how can we mitigate that?

I'd love to see commercial fusion reactor plants in my lifetime, but I don't think I'll see it. We're pretty close to seeing fission SMR plants really get going. As much as I hate AI shit, their data centers are power hungry af which has pushed these companies to think about providing their own on-site power to relieve strain from the grid, and these SMRs are kinda perfect for this. If we could see that scaled up or at least batched into array designs, we buy a lot of time to figure out fusion while shifting to a greener energy solution or at least replace the existing and very much aging fission plants we already have. And maybe SMRs can teach us something about fusion along the way.

Stay curious :)

[–] doomsdayrs@lemmy.ml 2 points 6 days ago

thank you! 💜

[–] peanuts4life@lemmy.blahaj.zone 12 points 6 days ago (1 children)

I'm sure a lot of very smart people thought of it for perhaps 30 to 40 minutes before deciding never to speak of that bad idea every again.

[–] doomsdayrs@lemmy.ml 2 points 6 days ago

I wish I was smarter in that field...

[–] jewbacca117@lemmy.world 9 points 6 days ago (2 children)

Diesel engines don't use spark plugs, they use pressure to ignite the fuel. What purpose would fusion serve here?

As for gas engines, why? Starting fusion reactions takes an insane amount of energy, we have yet to make one that produces more power than is put in. Spark plugs are much more efficient.

[–] doomsdayrs@lemmy.ml 2 points 6 days ago (1 children)

Updated post title to reflect your knowledge, thank you!

[–] jewbacca117@lemmy.world 3 points 4 days ago

I think you are missing the point of fusion as we know it.

Pistons are pushed by small controlled explosions a thousand or so times a minute. Each explosion pushes the piston, which makes the crankshaft turn.

Fusion, however is a continuous source of heat to produce steam that turns a turbine to make electricity. It's meant to be an alternative to nuclear power just with much less danger involved. Fusion can't melt down like nuclear. Fusion also would require very little fuel to keep going.

Unless I am missing the point of your update, I just don't think it's possible to make a fusion piston. I believe the only way is to use fusion to make steam to power a turbine.

[–] will_a113@lemmy.ml 7 points 6 days ago* (last edited 6 days ago)

There is one variant called Magnetized Target Fusion that kinda-sorta works like this, where the "cylinders" are made of liquid Lithium. On each "stroke" of the engine:

  • A rotating chamber of liquid Lithium is spun to make a cylinder of liquid metal
  • 500 pistons situated at the site of each spinning Li pool are precisely synchronized to push the liquid metal inward, turning it into a sphere
  • Fusion fuel (H plasma) is injected into the middle
  • The intense pressure forces the fuel to undergo fusion, pushing the pistons back out and distorting the Lithium back into a cylinder
[–] WoodScientist@sh.itjust.works 4 points 6 days ago

It can be done and has been researched. See Project Plowshare.

People who say we can't build fusion reactors are only partially correct. (And no, I do not mean that we can build tokamaks that are net energy negative.) We can build energy-positive fusion reactors, and we've known how to do so since the 1950s.

The idea was that you would build an enormous underground chamber. Then fill it with salt. Then detonate a small hydrogen bomb inside the chamber, instantly boiling the salt. You then run the salt through turbines to generate electricity. You power a city by setting off a nuke every one and awhile.

The results of this work were that yes, it seems possible to build a power plant that runs off of hydrogen bombs. We do in fact know how to build a fusion reactor today. The problem? Simple economics. This method just isn't cost-competitive with traditional electricity sources.

This should serve as a cautionary tale for those hopeful for the future of fusion or advanced fission concepts. It doesn't matter if you manage to build a tokamak that returns net energy. Ultimately it's just a cool science experiment. What DOES matter is if you can do it cheaply. And this is actually why I'm skeptical of fusion as a power source. Even if we do ever manage to make non-bomb fusion plants produce net energy, they would struggle to be cost competitive with renewables+batteries.

[–] cosmic_skillet@lemmy.ml 2 points 6 days ago

There are similar projects like this big fusion gun thing

https://www.youtube.com/watch?v=Q9VZ5b0Lwxk

[–] sylver_dragon@lemmy.world 2 points 6 days ago

It was kinda thought of in the '50s. Ford's concept the Nucleon was to use a fission reaction to heat water, which was used in a steam turbine engine. One of the issues folks worried about was, what happens in a crash? No, no one with a clue worried about a nuclear explosion, but the release of radioactive material would have been a real concern.

Some of this might change with the use of fusion. But, it's going to be a long time before a fusion reactor would be small/light enough to slap in a car. At the moment, we haven't really demonstrated a reactor which can commercially produce a net output of power. There has been some small scale experiments which technically produce more power than is used to initiate the fusion; but, that also relied a bit on an accounting trick (they only counted the energy of the lasers themselves, not the total energy used).

Also, when you get down to it, this is the ultimate goal of electric vehicles. Maybe someday, most of our electricity will come from grid scale fusion reactors. Those will charge the batteries which drive EVs. Moving the reactor into the car itself could happen some day. On the other hand, considering how poorly some folks maintain their cars now, would your really trust them to maintain a reactor? Again, not worried about explosions or anything silly. But, the release of radioactive material might still be a concern. It's probably safe to just use batteries and keep the reactors locked up in large facilities.

[–] tankfox@midwest.social 1 points 6 days ago

Get this if you put enough matter in one spot the mass of the matter acts as the piston compressing the material until it begins fusing enough to resist the inward pressure. This lasts as long as there are enough fuse-able materials in the mix, be aware they can get a little unstable when fuel gets low.

[–] jlow@beehaw.org -2 points 6 days ago

Because fusion is a scam.

[–] ianhclark510@lemmy.blahaj.zone 0 points 6 days ago

Imagine blowing a head gasket on your fusion powered Honda and having hard X-rays leak out from your hood