Rarefication

[MikeB]

what type of engine are you talking about that is easy/simple compared with Stirling/hot air?

What I meant was that with IC engines you can quite confidently state that during the combustion stage, the only relevant processes are expansion and heating.
In a steam engine or a jet turbine the various phases are physically separated - so you don't need to worry unduly about combustion affecting compression, etc.

With a hot-air engine, the cut-off between phases is very blurred, particularly where a regenerator is introduced, so a simple four-state model is really not adequate.

[Tom Booth]

....I’ve never seen a Stirling engine powered by molten salt of someone beats me to it, or already has, please share!

I haven't, and don't know of anything recently, but Infinia got a DOE contract to do research on some kind of thermal storage using salt.

https://www.researchgate.net/publicatio ... er_Systems


Someone recently sent me a sample of Erythritol mixed with graphite but I haven't had a chance to fool around with that yet.

[Tom Booth]

what type of engine are you talking about that is easy/simple compared with Stirling/hot air?

What I meant was that with IC engines you can quite confidently state that during the combustion stage, the only relevant processes are expansion and heating.
...

OK, but when I said: "... there could be more than one factor in play", that you quoted, that was all I was talking about. Different factors involved in the conductivity of gases as it relates to its expansion in an engine. Any engine or any situation really, just as a physical principle.

But yes, I agree, the overlap of the heating and cooling phases in a Stirling/hot air engine does present a problem that you don't have in other types of engines. But that's a different subject I think.

But actually you do, it's a timing issue. You have pre-ignition and such in IC engines.

If you, for example, cool and compress a gas it's conductivity increases, but if you heat a gas it's conductivity increases. What I meant was, different factors may be involved at those opposite extremes.

At the hot extreme it may be freedom of movement of single molecules, but at the cold extreme it would likely be something else, like transfer between tightly packed molecules.

[LES_Thermodynamics]

There is an interested type of Stirling engine called the horn engine, which has a large horn at the top with a narrow long body. It was made to test the idea of gasses expanding at the bottom due to heat and condensing at the top due to more space and cooler temperatures.

The only one that I’ve seen was a picture from a research laboratory and it was 6+ feet tall. I think that in order to effectively model the cycle of a Stirling engine you have to enlarge it to a grander scale. On smaller engines the process is very muddy and whatever you model is likely not applicable.