My contribution to the ECE

[matt brown]

I will try to make a new long stroke crank shaft for further testing. I wonder though, if this open cycle can be optimized for even more power than the Stirling cycle. I was imagining, perhaps, a sort of two stroke expansion pipe attached to the exhaust port that could force even more air back into the system each cycle. Or maybe there would be two pipes with check valves. One for exhaust and the other would be water cooled and only allow fresh cold air back in. I tend to think an optimized Stirling cycle would have more potential power.

You've made xlnt observations as you head down the Otto cycle path:

(1) longer stroke to bore ratio, but may cause volumetric issues between existing cylinder:displacer volumes
(2) aluminum or copper cylinder 'sink' is best
(3) open cycle (proof of concept) with BDC 'exhaust' port
and my favorite...
(4) snifter 'intake' valve on cold plate into displacer chamber whereby BDC port is ideally exhaust valve only

The Otto cycle has far greater power potential than the Stirling cycle due to a higher cycle rate potential. The main advantage the Stirling has is low thermal ratio potential and slightly better efficiency.

What's the current cylinder material?

[VincentG]

The cylinder and piston is borosilicate. The engine runs much faster with the port open. I will say after experiments with moving the displacer and piston by hand to simulate a much higher compression ratio, the hot stroke seems down right explosive. If the open cycle could keep that up at high rpm it would be quite the machine. That said, it has amazing LOW rpm torque in closed cycle mode. And now that I type this out....I'm picturing a dual mode engine. Stirling cycle for efficiency and then open the valve to run otto when you need to let it rip.

Matt, can you point me in the direction of any successful closed cycle otto engines?

[matt brown]

Sorry, Vincent, I've never seen ANY open or closed cycle ECE Otto design. Yes, there's some goofy stuff in the USPTO files, but nothing credible. Since Stirlings gained interest in 1970s, most ECE have hovered near Philips Stirling from 1930s. Most advances have centered around parametric studies and improving regen design. So, for quite some time, an ECE is nearly always considered some type of Stirling with a closed cycle where the dominant issue(to me at least) is the phasing issue regardless of alpha, beta, or gamma. Even suggesting an Otto ECE tends to raise the ire in the Stirling camp, especially when suggesting any type of valve. It's almost as if the ECE camp is trying to make their solution as different from ICE as possible. Meanwhile, I prefer to think similar ICE with fairly conv'l pistons, cylinders, slider cranks AND valves !!!

As I said about your hot bulb conversion, this is similar my type of thinking for the common DIY ECE most guys are after. There are several multi cylinder Otto schemes, but I prefer to focus on 1 cylinder schemes that nix phasing issues. As with your hot bulb mod, the open cycle is xlnt for proof of concept since it nixes cooling issues, and can be closed cycle when BDC ports are feed to cold reservoir (which also allows easy pressurization scheme).

In a world dominated by simple ICE designs, it should be obvious that ECE should parallel ICE whenever possible, but that doesn't bring in the grant moola. BTW have you seen this video for an Otto-Langen reproduction ('atmospheric' Lenoir cycle engine like Otto was adjusting vales on when his eureka moment changed history).

https://www.youtube.com/watch?v=QlxB5WraXNM

[Tom Booth]

(...) BTW have you seen this video for an Otto-Langen reproduction ('atmospheric' Lenoir cycle engine like Otto was adjusting vales on when his eureka moment changed history).

Basically seems like a canon, with a gear rack attached to the cannon ball/piston.

Expansion is entirely explosive. Charge it up and fire it off.

I would suggest VincentG that perhaps your cam mechanism should follow the same principle. A brief (explosive) blast of heat introduced at TDC. The displacer making a very quick rise and fall, maybe somewhere between 0 to 90 degrees BTDC (experiment).

The rest of the cycle being "dwell" the displacer just sitting on the hot side waiting for the flywheel/crank to come back around to TDC. (No cold side dwell whatsoever).

Basically what I was trying to achieve with this:

https://youtu.be/MiX8Pttid6o

Your mechanical (cam) solution would be much easier to "program". The curve would be basically just a circle with a "bump" near TDC.

Resize_20230307_033030_0406.jpg (102.44 KiB) Viewed 3280 times

My theory being that heat is introduced by agitation of the air, both when the displacer rises up, and ALSO WHEN IT FALLS.

As the displacer falls the air is forced across the hot plate AGAIN. That IMO is why a Stirling "ignition" is anything but explosive. The heat input is too washed out almost across the entire cycle.

The magnetic type displacer behaves similarly at high RPM. The displacer just jumps a little at TDC and just rests at the bottom the rest of the cycle. This brief jump of the displacer at TDC seems to work quite well in practice, the magnet flies past so quickly at very high RPM, the displacer on that type of engine barely seems to even move.

Also, make the bottom of the displacer something that can absorb heat while at dwell, releasing the heat when it "jumps up" at TDC, so the heat is released by BOTH surfaces. The hot plate on the bottom of the engine AND a second hot surface on the bottom of the displacer.

Some SMALL holes (about 1/8 inch diameter) in the displacer would cut down on drag and produce jet streams that would hit the hot plate.

An IC engine doesn't need a "cold side". If that is what we are trying to emulate, Just an explosive ignition. I don't think an EC engine actually requires a cold side either.

That is the displacer movement I was going for with that Arduino program, but your cam arrangement would, of course, be much simpler, at least for testing as proof of concept.

Of course, I could be wrong and it might not work, if a long "dwell" on the cold side to let out the heat to the "sink" is really necessary. Personally I think that is complete hogwash. The heat is CONVERTED to power output, so it only has to be let in at TDC not let out, ever. Not as heat anyway. It is let out as torque/power/mechanical rotation.

[Tom Booth]

Of course, by TDC I mean full compression. In an LTD that would usually be when the piston is all the way downward.

Also, it might be worth mentioning, that Arduino setup, like those magnetic engines, has an acrylic "cold side".

The last thing you really want is a "sink" on the cold side sucking out the heat as fast as you can introduce it, before it can deliver power to the piston. The "cold side" is acrylic, non-metic, non-heat conducting.

[VincentG]

This is exciting stuff gentleman. Is there any animation of the operation of the engine you posted Matt?

Tom, that arduino control looks promising. Did it ever run?

I have through some quick testing, been able to operate the engine in sort of a hybrid open/closed mode by making the hole smaller. There is still an exhausting of hot gas, but there is now a powerful cold stroke. It seems to combine the higher rpm of the open cycle with the low rpm torque of the closed cycle all at the same time!

I will add a copper plate on the bottom of the displacer, and modify the cam to have a shorter duration. Clearly with all of these further mods, I would need a much bigger working cylinder to utilize all of the added hot air. Though maybe I will add an intake reed valve on the cold plate as Matt suggested to eliminate the need for added cooling.

I imagine the ideal setup would have an exhaust port that is a bit before BDC, the piston would then continue past, using all the hot air until it starts to be expansively cooled. Then the reed valve would let more air in at the cold plate, just before the piston starts back down to start compressing a now fully cooled charge of air. It seems the power potential of this system is even greater than I expected.

[Tom Booth]

...
Tom, that arduino control looks promising. Did it ever run? ...

Short answer: No, Never got that far. Never had the time.

Ultimately the idea was to have live feedback from RPM and whatnot for a kind of fine tuned "electronic ignition"/displacer control.

The little servo that came with the Arduino, I thought was too slow and weak for what I ultimately had in mind, so the idea was more suggestive than actual. A possibility for others to consider.

I got as far as learning how to program the Arduino just enough to get the basic motion I thought might produce the greatest power and efficiency, but your cam for production, would be better. Less to go wrong or break.

But making it programmable for testing would save having to build a new prototype for every minor change or variation while experimenting with different timing scenarios, possibly even live reprogramming while the engine is running.

I got distracted just trying to find a more responsive servo, then by other projects. That's a project for someone with a lot more robotics type programming experience it would take years for me to learn. Or for someday when I have more time for such things

[Tom Booth]

...

I have through some quick testing, been able to operate the engine in sort of a hybrid open/closed mode by making the hole smaller. There is still an exhausting of hot gas, but there is now a powerful cold stroke. It seems to combine the higher rpm of the open cycle with the low rpm torque of the closed cycle all at the same time!

Interesting how controlling the exhaust port size just right could have such an effect.

I suspect, though, that the same result could be obtained by just lengthening the throw slightly, of maybe increasing the piston diameter.

I think energy is being wasted just pushing hot air out against atmosphere when that same "work" could be just as well pushing the piston that much more further or harder (indirectly against the same atmosphere). Adding an additional load might work also, but having a kind of variable size port outlet for no-load conditions, especially seems like a reasonable adjunct, perhaps

[VincentG]

Agreed Tom. There is not enough working volume to utilize the hot air. A problem I am happy to have instead of the opposite.

[Bumpkin]

Hey Vincent, it’s interesting that you’re looking at wood power and maybe using a 55 gallon barrel. I’ve got a barrel in my shop dissected and about ready for reassembly for the same purpose, to replace in the same foot-print my current shop-stove, and cogenerate a bit of charge for my solar battery through dark spells. I’m inserting a heavier gauge stove-top/chamber-bottom, shaped in a shallow cone for strength, to match the similar shaped displacer and Beta piston above it. About the bottom third of the barrel is just an empty ring to raise the firebox from overheating the floor and to give a convenient feed height. The top third of the barrel is the engine bore, but the thin-as-possible displacer (1/2 inch or less?) will only stroke about 3 inches and the power piston only about a half inch. The rest of the wall height would support a bicycle inner tube rolling-seal for the Beta piston. The displacer will fit the bore as close as possible and be entirely flow-through, to alternately blanket the hot and cold ends. I think the value of radiant transfer is very under-rated. One side of the blanket would be a flow-through air heater, being itself heated radiantly by the hot end of the chamber. The other side of the blanket would be a flow-through air cooler, being itself cooled by radiating heat to the cool end of the chamber. The inner thickness of the blanket would be a flow-through regenerator and a conduction insulator.. Anyway, that’s the current plan, but it seems like every time I get back to it or find some new bit of scrap-yard obtainium, something changes. If I ever get far enough I’ll post my own thread, but meanwhile I thought maybe some of that might relate to your direction. Best wishes on your project,

Bumpkin

[VincentG]

Bumkin, sounds like an interesting project. You should definitely start a thread about it. I'm curious how you construct the rolling seal. I think that may be the way to go for a large scale easy to assemble engine.

I have decided that in the interest of saving time, instead of engineering a completely new small engine, to redesign the little LTD into a more modular and efficient platform for testing. I found that the bolts that hold the two plates together are a significant thermal bridge between the two plates and needs to be addressed. The other major problem I see is that the bottom hot plate is bigger than the displacer. This means that the displacer can never fully "shut off" the heat source. Lastly, I think the entire engine should be cooled, save for the hot plate and the hot plate on the bottom of the displacer.

Through the magic of CAD and 3d printing, this is almost easier done than said. Here is the new fully water cooled housing design. The bottom plate will now be .120 6061 aluminum, siliconed to the housing and smaller in diameter than the displacer. The top plate will remain stock for now. The walls of the housing are surrounded by a water jacket that extends up past the cold plate as well. Set up with a gravity fed water system this should provide much better cooling and a much faster hot plate response.

The fist pic is just a section analysis to better show the water jacket. The circular passage is just a means of saving print time and filament.

new housing section analysis.jpg (325.1 KiB) Viewed 3222 times

The full housing. Roughly a 2.5 hour print using nylon that can handle upwards of 300 degrees F. The hot plate will sit down on the bottom most ring and allow a small space above for the displacer attached hot plate. The outer ring of the displacer will then sit flat against the bottom of the housing, fully insulating the heat plates while at rest.

new housing cad model.jpg (234.93 KiB) Viewed 3222 times

[matt brown]

Vincent, the only animation I could find currently is

https://commons.wikimedia.org/wiki/File ... mation.gif

but there used to be a more detailed one online. This was the world's most efficient ICE in early 1870s when steam was dominant. The stats go something like this...1860 Lenoir eng with 4% eff vs 1867 Otto-Langen eng with 12% eff. Prior later Otto eng (compression cycle), most eng guys were mechanics with a hands on approach from observations devoid basic thermo understanding. Knowing the history of all this 'rusty iron' prevents one from running down a well worn, but fruitless, path. I've been studying thermo & engs for 50 yrs and can guarantee that there's little wiggle room left...

[Tom Booth]

... I found that the bolts that hold the two plates together are a significant thermal bridge between the two plates and needs to be addressed. The other major problem I see is that the bottom hot plate is bigger than the displacer. This means that the displacer can never fully "shut off" the heat source.

I think these are both excellent ideas.

The next I'm not so sure about:

Lastly, I think the entire engine should be cooled, save for the hot plate and the hot plate on the bottom of the displacer.

Nylon should be a rather poor conductor of heat either way, so water cooled or not, it might make little difference.

The design theory I've arrived at is primarily based on the kinetic theory. The heat going into the gas, the gas "expanding".

In theory, this expansion consists of millions/billions/trillions(?) of molecular collisions.

The goal then is for there to be no energy loss before the molecules collide with the moveable piston and transfer energy to the piston in the form of motion.

Any cold surface along the path between the hot plate and the piston, then, is a potential energy drain.

However, nylon is a very poor heat conductor, so even being water cooled would have difficulty transferring much, if any heat across to the water in the fraction of a second it takes for the engine to complete a cycle.

IMO you would probably do well to make the entire engine body out of nylon, except for the hot plate, similar to these engines, though these are acrylic:

Resize_20230308_034156_6682.jpg (79.67 KiB) Viewed 3198 times

Of course, many (probably most) people consider my theory; that no heat sink is a good heat sink; radical, unsubstantiated "pseudoscience" etc. But hay, those little unibody all acrylic engines (except for the bottom hot plate) run great and stay quite cool on top, which I think proves my point, having had this one running on hot steam for three hours straight, without ever overheating.

https://youtu.be/l2XcnN6QdfA

[Tom Booth]

Of course, I'd be very interested in the results of a comparison run of your setup, with vs without cooling water, and the effect of different cooling water temperatures.

The engine may indeed run "better" with cooling, but possibly for reasons similar to having a vent or port. The larger ∆T allowing more opportunity for expansion without the cooling water actually absorbing heat from the working fluid, though the cooling water taking in heat from the ambient surroundings is possible, if the water is below ambient.

[VincentG]

Tom, I am starting to think as you do, in that the cold side may not be necessary for cooling the air in a theoretical perfectly insulated engine, that ALSO has enough working volume to start into expansive cooling before compression. I think the main reason the cooling jacket is needed is to prevent the heat source from bleeding into the rest of the engine, and reducing efficiency that way. It seems that heat is added to the system much faster than any cooling(save for expansive) can take it away. I tend to think this is an affect of the speed of radiant heat entering the system when the displacer is lifted, which should be increased further by the addition of the hot plate mounted on the displacer bottom.

If we reduce the "on" time of the displacer to only 90 degrees or so, the air will be in contact with the rest of the internal components most of the cycle. So reducing the heat added here by thermal bridging should be a significant improvement to delta T.