I wonder if you’d get issues running an ICE under water if you went very deep, due to pressure changes on the exhaust system. Assuming you could seal up the system well enough to work at depth, and provide O2 as you mentioned.
Even the pressure going into the combustion chamber could be a complicated thing, right? Say you’re at 20 feet, that’s a fair amount of pressure. But what if you’re at 80 feet? Would it still be able to function the same way? I assume no, but I also know nothing about running ICEs under water.
If you can push the fuel and air in at ambient pressure, it shouldn't matter much right? Because the 'neutral' point of the cilinder pressure would be just as high as the pressure of the exhaust.
You'd probably lose some efficiency because the difference between peak pressure and neutral pressure in thr cylinder feels like it would be smaller. Perhaps not, because you could fit much more fuel and air in the cylinder for a bigger bang?
All of your densities would be higher. Input, chamber, and exhaust would all have proportionally higher pressures and use more air. (And gas? I don't know if it's aerosolized or vaporized.) In theory this should all cancel out, although the absolute pressures and variable reaction rates and friction probably cause issues.
Even the pressure going into the combustion chamber could be a complicated thing, right? Say you’re at 20 feet, that’s a fair amount of pressure. But what if you’re at 80 feet? Would it still be able to function the same way? I assume no, but I also know nothing about running ICEs under water.