Ok. Let’s call it the expansion/contraction ratio. Compare the total air volume of the engine with the power volume expanded; to the total air volume with the power volume contracted. Don’t count air-tight displacer volume. Do count dead space including exchangers, regenerators etc.
Look up “Boyle’s law,” and know that for most of our purposes air can be considered a “perfect gas.” So the expansion/contraction ratio tells you how much temperature difference is needed in the working air just to break even, but heat won’t flow in and out of the working gas without a temperature gradient. My own totally unproven rule of thumb; is that to expect a well-designed engine to run, it would need at least twice the exterior source/sink temperature ratio, as the engine’s internal expansion/contraction physical ratio. Look up “Absolute temperature,” and remember to measure with a zeroed scale.
Once you get past the temperature difference/volume difference ratio, then the variables start to get interesting, but to that point I think we’re mostly on common ground.
(I’m open to debate, but to possibly head off our esteemed purveyor of verbiage; yes of course power out of a heat engine is heat out of a heat engine, but the engine needs to run first.)
Bumpkin
Sorry for the wasted time, but for my part it’s good to know. Had to watch the animation for a while to see the why.