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
No idea why noone mentioned it, but this exists.
https://generalfusion.com/
The core idea of combustion is using momentum to achieve combustion to generate back momentum (and heat).
The laser fusion detonation is similar, but I find other concepts reflect the idea way better.
General fusion uses liquid metal, that is compressed into the center trapping a bubble of fusion gas under extreme pressure for a moment. Inspired by cavitation bubbles in water that when symmetric enough can produce light and evaporate metal.
The fusion then bounces back onto the liquid metal, and fusion products are absorbed by it, so the heated liquid can be cycled into a heat engine. I don't think there is an intention to recover mechanical energy though.
Another approach is dynamic z-pinch. Helion would be an exanple.
You form a magnetic enclosure trapping fusion gasy then push the magnetic enclosure inwards, compressing the gas to fusion. The charged fusion products (needs fusion that doesn't emit neutrons) are again trapped in the field, pushing against it with far more speed, effectively far higher temperature, causing the field to exoand again against the controlling magnetic coils, that now operate in reverse generating current from regeneratively breaking the push.
I think this is the closest analogy to combustion engines. An initial push is inserted via momentum (of the magnetic field), which compresses the fuel, combusting it, increasing pressure/temperature, pushing back against the confinement which now absorbs the (magnetic) momentum, turning it back into power.
The only difference is that between cycles the power to keep the next cycle going is stored in capacitors not as momentum of something. And ofc the thing in motion is a more intangible magnetic field, together with currents running in magnets, not physical mass.