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Matt, I think the adiabatic cycles would be best gamed by considering displacer chamber maintaining Tmax to simulate a valve in the conduit. In other words the pressure would be maintained in the displacer cylinder but it would not keep adding heat as the power piston expands and adiabatically lowers temperature of its isolated volume of gas.

You mean something like this...

(1) a valve in conduit between DP and PP opens to transfer gas
(2) said valve then closes
(3) PP gas expands adiabatically

Now the hard part...

After (2) there's less gas in DP then prior (1), so how do you replace this "lost" gas with less Wneg during compression than Wpos during expansion ???

My last graphic could be as you suggest simply by adding a valve in conduit between hot side DP and PP for Essex C or D (and nixing regen). In effect creating a low end Otto cycle where the DP "oscillates" between a Tmax and Pmax reservoir during expansion and a Tmin and Pmin reservoir during compression.

You mean something like this...

(1) a valve in conduit between DP and PP opens to transfer gas
(2) said valve then closes
(3) PP gas expands adiabatically

Yes.

Now the hard part...

After (2) there's less gas in DP then prior (1), so how do you replace this "lost" gas with less Wneg during compression than Wpos during expansion ???

Don't need to give you any extra work but it could be gamed where pressure in DP after it drops to Tmin could be less than pressure trapped in PP after expanding to BDC. Then when valve opens again this pressure differential drives partial "free" compression into DP(while PP is dwelled at BDC), recovering lost energy from (thermodynamically)incomplete PP expansion.

This makes more sense if final temperature of PP at BDC is above 300k.

I was gaming something very similar with Essex which led to last graphic, here reduced to the 2 air versions


I chose to post original graphic since these 3 cycles compare well for small volume ratio, but my original game was trying to bypass regen after PP and feed gas directly to DP curious over PVT values. My game was whether any potential PP heat loss after expansion could be simply dumped in DP cold side and not "lost" since this would also reduce input requirement after DP reverses gas to hot side.

Anyways, I get your idea...simply make P at 1 less than P at 4 via adjusting PVT values thruout cycle. Note that in above graphic, this valveless scheme will 'drain down' DP more than your valve scheme would. Thus, after PP expansion, P in DP of valve scheme would be greater than P in DP of valveless scheme. I'll play with DP/PP ratio later tonight and see if I can fix this.

VincentG wrote: ↑Mon Sep 30, 2024 7:12 pm This makes more sense if final temperature of PP at BDC is above 300k.

Indeed, and now you can see where I was going with simply dumping PP "waste heat" directly to DP cold side. Obviously, this favors a larger DP/PP ratio than this DP/PP=.5 example, so I'll start with DP/PP=1 while gaming P swing and T swing in DP vs DP and PP volumes.

For the time being, let's assume there's an annular regen in DP and that the P values thruout cycle are the main focus, not regen efficiency. This is the beauty of scheming Otto where various events that would tax efficiency in other cycles merely tax Otto output. The premise here is Otto akin ideal gas spring where output is simply heat in vs heat out. Yes, Carnot get his cut, but Otto avoids compounding inefficiencies.

Indeed, and now you can see where I was going with simply dumping PP "waste heat" directly to DP cold side. Obviously, this favors a larger DP/PP ratio than this DP/PP=.5 example, so I'll start with DP/PP=1 while gaming P swing and T swing in DP vs DP and PP volumes.

For the time being, let's assume there's an annular regen in DP and that the P values thruout cycle are the main focus, not regen efficiency. This is the beauty of scheming Otto where various events that would tax efficiency in other cycles merely tax Otto output. The premise here is Otto akin ideal gas spring where output is simply heat in vs heat out. Yes, Carnot get his cut, but Otto avoids compounding inefficiencies.

I see. Impressive how much efficiency gain comes from shrinking size of DP. Makes you wonder what everyone has been chasing with huge DP volumes...

Do you mind me asking what a valvular displacer is?

Fool wrote: ↑Wed Oct 09, 2024 2:33 am Do you mind me asking what a valvular displacer is?

By valvular displacer, I mean a component that not only displaces gas, but also serves to shut off the flow of gas from one side or the other. In other words, the displacer moves gas to the hot side while at the same time preventing any gas from flowing into or out of the cold side.

This is why a short stroke and transit time seem beneficial. Wasted energy is flowing through the gas any time the displacer is in motion and not acting as a closed valve.

The best displacer IMO would be able to cover the cold plate before exposing the hot plate, and vice versa. The mechanical complexity of such a device is not warranted for at least my purposes but would hopefully be realized at some point.

Got it. Thinking about it.

VincentG wrote: ↑Wed Oct 09, 2024 5:53 am
The best displacer IMO would be able to cover the cold plate before exposing the hot plate, and vice versa. The mechanical complexity of such a device is not warranted for at least my purposes but would hopefully be realized at some point.

I was working on a graphic of an open cycle DP to show P values dominate a cycle scheme when another "flash in the fog" crossed my path. I stopped here, evolving the PVT issues when adiabatic expansion for an air cycle (fixing T vs fixing P). Prior this graphic, I was jumping around others, looking for something I could recycle to save time. OK, so that's the back story, can anyone spot the 'novel' DP that was my flash in the fog ???