Quote:
Originally Posted by elhigh
One wonders if you could do a sort of super-Atkinson cycle, like a 2:1 ratio instead of the 1.3:1 ratio of current modified Atkinson cycles. If you're injecting only a tiny amount of pure oxygen and a small amount of water to do the expanding, how much air you compress during the compression cycle wouldn't matter so much, would it?
Compression stroke = 40mm, expansion stroke = 89.4 (for instance).
If you're using water injection for expansion mass, that'll absorb a tremendous amount of heat. Could you do away with a radiator (and all its associated parasitic losses)?
Hmm, maybe not all. You'd probably want to reuse that water, or else have to carry around a large/heavy tank full of water. So a condenser is needed, aka a radiator. Dang it.
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The direct injection of pure oxygen and fuel/water means you do not need an intake valve. You could run the engine as a two stroke. Yes, under full load, you can inject your oxy/fuel/water to maximize temperature and pressure. But, you then have the option under light load to inject the minimum oxy/fuel/water and derive as much energy from it by over expansion. By using over expansion, it makes it easier to condense the water and reuse it. The ability to carry oxygen is the main limitation to this idea.
ReDevil's idea of a small single piston engine is very doable. Originally, ceramic pistons, cylinders and heads were specified. However, using water as our expansion fluid means we can control peak temperatures. Ceramic coated parts would probably work. With no nitrogen present in the combustion chamber, we can run hotter than the 2300 degrees C temperature of formation for NOx to achieve higher theoretical efficiency while tempering maximum heat load via our water flow.