VincentG wrote: ↑Thu Jul 11, 2024 7:37 am
Well talk about a textbook Stirling cycle.
If you have a textbook anything like this, please share. To kick this can further down the road...
- TX vs EX hot PP beta.png (21.43 KiB) Viewed 3480 times
where TX represents unknown "textbook" hot PP beta vs EX represents my "Essex" hot PP beta. Both are 300-600k cycles with zero buffer pressure (aka vacuum). Furthermore, both are depicted as ideal everything with double dwells.
Although both are betas where DP and PP overlap, TX has an irregular motion DP vs PP which I'd characterize as DP leads PP by 270 deg (from PP at TDC). Meanwhile EX has a regular motion DP vs PP which I'd characterize as PP leads DP by 240 deg (from PP at TDC). Now, the fun part...TX has a 90deg dwell for DP and PP vs EX has a 60deg dwell for DP and PP.
TX has an obvious flaw where DP stroke exceeds PP stroke, but let's ignore that major caveat. Instead, let's focus on the similarities where both have the same Carnot efficiency from the same 300-600k thermal cycle, but EX produces more power from greater expansion (don't let the 2 red bar max fool ya). The main difference thermally between these 2 is TX process C vs EX processes C1-C2-C3. For EX, C2 process (180-240deg) could have DP 'run all the way over' to PP at BDC, whereby at 240deg, P=.66 bar vs .8 bar per graphic, but this would screw up the otherwise regular motion. However, if .66 bar at 240deg, then C3 work = 1neg and Carnot=.50 so .80 bar at 240deg looses a tad to Carnot. This difference is denoted by the question mark, but really just hair-splitting.
An interesting takeaway is that during C3 process, no backwork would yield Carnot=.66 yet the most ideal "tiny" .66 bar to 1 bar compression sinks cycle to Carnot=.50
If EX looks textbook, it's because an ideal 60deg dwell approaches the real far faster than any ideal 90deg dwell.