[bobkoure]

Originally Posted by bobo5195

I assume your talking about stratified (areas of fuel surrounded by air) engines (not commonly used as there are problems with NOx, most modern (SI - spark ignition) engines don’t work like this (although a lot of older ones claim too)

Actually I was talking about diesel engines as (AFAIK) SI becomes problematic when your cylinder head is hot enough to produce premature combustion. Yes, NOX is still a problem (I'd imagine it would be a bigger problem). And I was more thinking along the lines of turning poor scavenging into a "feature" - so really unscavenged exhaust with a pocket of air, into which a bit of fuel gets squirted.

Increasing turbulence is an engine design goal. Engines contain some of the most turbulent flows that you will ever find.

Yup. Actually know a bit about this (probably 'way outdated, though). However to move to something like adibiatic (or near adibiatic) IMHO all the "rules of thumb" (things like flow management, combustion area, head shape, rod length ratio) IMHO go out the window.

The reason is your typical flame has a combustion speed of 0.6m/s (ideal speed) however this is not fast enough to allow good combustion (7000rpm do the math on cylinder sizes).

We were at more than double that - the answer at the time was to introduce multiple flame fronts (very rapid series of sparks). Not sure why that didn't catch on...? At the time CDI was exotic, but certainly it isn't now.

To increase this engine designers increase turbulence and use swirl

Don't forget squish.
The point is that adibiatic shouldn't be approached as current technology with a few parameters tweaked.
IMHO a lot of IC technology has been developed through racing - but racing isn't just one technology - and it gets steered the racing rules in effect. For instance, at one point in IC evolution, there was a turn from slow revving, lightly built large displacement engines to more heavily built, faster revving ones. From my reading (not old enough to have been there) the race cars with that lighter-built design lost a major race through petcock failure - and there was a strong suspicion of sabotage. Anyway, at that early point, a simple lost race or two might be enough to turn development in a different direction. Now we have displacement rules, which tends to drive faster revving engines
Maybe it's time to try that "other branch in the tree". ...and maybe it's time to chase something other than the sterling cycle. Maybe fuel cells - and maybe something else. External combustion reciprocating has advantages in the air pollution area and has a useful-for-daily-driving torque curve. Then there's turbines, which other than a short drive in a GM prototype in '64 I have no experience with. The problem at the time was the transmission (manufacturing costs)... They probably sucked at fuel economy, threw lots of hydrocarbons out the tailpipe, and likely were bad in other ways that nobody knew/cared much about then

Shift reactors... hmmm... interesting - clearly I've been out of that loop for 'way too long (dropped ICs for PCs in the early '80s, combination of having lost a couple of good friends on the track and having fun cobbling together electronics for engine management systems - laughably crude in retrospect.) And ya have to wonder if this same reaction (as well as lower temps) might be a factor in water injection reducing NOX. Did a bit with it, until the rules changed and it was "cheating". At the time we were after the greater "push" from water vapor expanding - and we could run higher compression ratios without detonation - and without using "illegal" fuel (rules again). And we didn't care about NOX.

Space stations? I want to visit some other planets.