60L drum medium temp Gamma build

[VincentG]

Thanks, I agree that in a running engine the chamber would have better temperature distribution and likely perform better. It does seem to improve with a few cycles.

I will try to face the displacer ends with aluminum foil like I did in my epoxy chamber.

I do think the gas temperature is being greatly influenced by the displacer and chamber walls.

If I allow the air to escape the chamber, it is very cold, indicating it is slipping past the cold plate still.

I have not yet ported the displacer to prevent this, that will come after the foil test.

The top plate is already flexing quite a bit. .5psi across a 14" diameter is 75lbs of force. So it will need stiffening.

I should be able to run the chamber up to and above 200 degrees. Maybe an on demand electric hot water heater will do the job.

[VincentG]

I faced both ends of the displacer with foil to no change. If anything it's a bit worse. Probably because the hot end of the displacer does not directly contact the hot plate like my epoxy engine, so the foil never reaches Tmax. It then acts to lower gas temp even more than without.

Though the bottom of the displacer seals well against the foam ring, the top of the displacer does not seal well to the cold plate due to the plate not being flat. I will try to add a sealing ring around the perimeter. This should help quite a bit.

Either way, the larger problem is the huge surface area of the displacer and chamber walls. I will try to section 6 inches from the drum. This will leave the displacer only one foam board thick.

Even just one 2" foam board should provide plenty of thermal separation from top to bottom.

[VincentG]

I am planning and looking forward to trying this chamber with cold water in the lower heat exchanger and solar heat above. Maybe at this larger scale the buoyancy effect is large enough to make a difference.

The results of cold water(55F) below and ambient(85F) above were surprisingly good already.

In this configuration, the upper side walls of the chamber will be effective heat sinks as well so I'll try this before I shorten the chamber. Of course, as I'm typing this, I realize the whole chamber could be ran upside down.

[VincentG]

I've painted the upper half of the chamber flat black to test with solar heat on top and cold water below. It works quite well, the upper plate reached 135F in mild sun and the walls were 95F. After letting the chamber sit for 1.5 hours with the water shut off, it still operates well.

With this setup the displacer needs a ring half way up and two sealing lips fixed to the chamber walls to isolate either end of the chamber better. I'm happy enough with this for now that it's time to start work on the rotating assembly and see what it can do.

60l drum ambient heat.jpg (278.26 KiB) Viewed 4213 times

[matt brown]

I can across this graphic from last summer and gave it an update

Vincent 60L.png (7.04 KiB) Viewed 4166 times

The old version was aimed at open cycle with Otto cycle. The new version is aimed at closed cycle with more of a "green" cycle. In this update, I'm pitching fully insulated DP with cold sink at PP only (and bash valve to nix pressure lock). Either way, we probably both see that DP would be banging into ends without some soft cushion in DP ring area.

Green cycle PV.png (11.68 KiB) Viewed 4166 times

Hopefully you can read into this graphic some actual dP and dV values

[VincentG]

The chamber really likes solar heat above and cold water below. After adding a 3" pipe nipple to concentrate the air, it's a solid little blast in the face when I release the pressure. The air is nice and warm this way. With heat below and cold above, the pressure pulse is always very cold, obviously losing effectiveness. I've also ported the top of the displacer similar to my epoxy engine, to provide the gas a path to the bung even with the displacer obscuring the plate.

I just got back from a day out exploring the Catskills, the chamber was sitting out in the beating sun all day after being left from the night before. There was enough temperature difference to operate.

If this chamber can maintain isothermal compression, it could easily get away with a 1:1 DP:PP ratio even at this low delta T. I'm thinking the flywheel should be geared up from the crankshaft so a lighter flywheel can hold a higher RPM and keep power pulses smoothed out nicely without being too heavy.

The crankshaft and bearings will simply be an old lawn mower deck spindle and pulley. The pulley end can belt drive the flywheel/load and serve as the PP crank throw. Most pulleys have a 12 point spline drive which should allow easy phase adjustment. A cut down mower blade should work well for the displacer crank throw. A simple steel upright from the reinforced drum lid should be all that's needed. Then the whole rotating assembly will be a nice modular setup to easily swap between different chambers.

[VincentG]

Matt I really like the idea of a green cycle after you bringing it up last time.

[Fool]

VincentG, It's a beautiful thing.

Matt, The green curve looks like a pseudo Carnot cycle with rounded ends. It starts out isothermal then peels off for an adiabatic line.

[VincentG]

I'll follow this up with some thermal video, but after some testing it seems that everything is a "regenerator". The thermal mass of solids is so much higher than gas that nearly every surface acts as a regenerator, even when not wanted.

The only material that resists this significantly is xps, at least from what I have seen. I have some aerogel to test but it's nasty dusty stuff that I have no interest in using.

Any other material sucks heat out of the gas far too fast. For a higher temperature engine, this doesn't appear as significant as the higher delta more easily overcomes the heat sink effect. In a low temperature engine, more care is needed.

On a side note(maybe), I've found that the outside surface of my fresh cucumbers stay over 5 degrees F cooler than ambient, even after sitting for hours in the same environment. Online sources say internal temperatures are up to 20F lower than outside. "Cool as a cucumber".

[matt brown]

Sorry about that last graphic, it was rough on the eyes due to being sequenced in squares.

Hopefully, you see this before you make any radical moves...

Vincent ECO.png (10.77 KiB) Viewed 3972 times

Here's a clean version of past graphic with a few mods that I labeled ECO for external combustion Otto. This is one of my ancient Cv reservoir schemes, but my past scheme was for res connecting conv'l 2 stroke ICE donor engine. That scheme was crazy since valve mech was too large for 'high speed' scheme, but here, things are low speed. Enjoy the nickel tour...

(1) compression ratio is vols (A+B)/B
(2) which is probably best between 2 and 3
(3) cycle can be Otto or Green
(4) both will require cooling at PP cylinder
(5) cooling can be via open or closed cycle
(6) top sequence shows common stroke and 180deg double dwell

With this scheme, vol C is irrelevant and serves merely as massive thermal reservoir - note partial DP sweep (no need for full sweep). Furthermore, with this scheme, the entire reservoir is insulated (no cold plate) and the only cooling is via PP cylinder. Since a body in motion tends to stay in motion and a body at rest tends to stay at rest, frame 4b is an option where some slight of hand provides PP continuous motion (nix pesky 180deg PP dwell) via an old world "overshot" stroke with a long Rider style piston (requires common stroke). In this manner, only DP has dwell, but some quality quite time should reach unshown frame 4c. The only bugaboo for this scheme is that pressure lock must be avoided via bash valve atop piston crown or some other means.

Nice to see someone building an engine !!! I'm playing with some numbers (wink-wink)

[matt brown]

VincentG, It's a beautiful thing.

Matt, The green curve looks like a pseudo Carnot cycle with rounded ends. It starts out isothermal then peels off for an adiabatic line.

The "green" cycle crops up every 10 yrs or so and that PV is from a recent paper (cute how the work area is green). I've always had a fondness for this cycle since it can run lower thermal ratios than standard Otto. I consider it nearly midway between similar Stirling and Otto, but comprising more of both cycles advantages than disadvantages. It might have less efficiency than Stirling, but it has a far faster cycle rate without isothermal, regen or dead space issues. The only major bugaboo is Cv input which I've spent many years gaming (no ICE issue but major ECE issue). Due to that adiabat, it's fun gaming monatomic vs diatomic schemes.

BTW have you seen the wiki read on Cheng cycle ?

https://en.wikipedia.org/wiki/Cheng_cycle

This is the type of stuff I was into back in my steam days. I don't follow much 'weird' stuff anymore, just some edgy ICE stuff like argon injection and acetone fuel (synfuel fanboy back in the day).

[VincentG]

As much as the green cycle seems ideal, I still can't think of an easy mechanism to get it functional.

The best I can figure is two separate displacers operating on the same axis, one for the hot plate and one for the cold plate.

Compress the gas into the cold plate, cover cold plate, expose hot plate/heat gas, cover hot plate(cold plate still covered), expand gas, repeat.

Two separate displacers and two separate control mechanisms. Not impossible but not easy.

I've already learned with my ring cam LTD that you can't expand hot gas into a cold space, it loses all it's energy too quickly.

[matt brown]

Indeed, heating AND cooling the same cylinder is a no-go and ideal cold PP gamma nixes this issue via regen prior PP.

1x vs 2x DP.png (6.89 KiB) Viewed 3871 times

This layout is akin tin can model where PP is 'between' hot and cold plates since it lacks regen. This basic config is worth consideration where ideally everything would be non conductive except both hot and cold plates. Eng A has typical one DP vs eng B has two DP. With DP dwell, the DP/PP volume ratio (of both) is unconstrained, whereby the green cycle could use a long piston stroke to drop both pressure and temperature AFTER hot DP closes off hot plate. This would lower required cooling from cold plate which could 'save itself' for cooling gas during 'isothermal' compression from said long stroke.

How's that for easy-peasy (except DP dwells)...

[matt brown]

But wait, there's more...

2 reservoirs.png (7.51 KiB) Viewed 3850 times

To increase cycle rate (rpm) let's add some reservoirs to nix source and sink bottlenecks

which starts looking real familiar...

heat vs work.png (62.51 KiB) Viewed 3850 times

but wait, there's more...
(1) both displacers can be driven from piston mech
(2) 'return' spring on each displacer will nix typical inertia work loss

back up a couple comms to my ECO engine graphic with "overshot" piston where unshown "4c" holds the magic...

[VincentG]

Golly Matt you sure have tons of goodies up your sleeve. At least this drum build will be relatively easy to change/modify. My continued beef is that the more ideal the cycle gets, the less ideal the implementation gets.

My current realization is just how damn fickle the gas is, especially at these low temperatures. Although I guess the reservoirs do well at keeping larger volumes of gas at the right temperature.

Maintaining gas temperature throughout the cycle is like trying steer butterflies down a path, when they can barely fly straight on their own.