Pressurization & Lubricating oil

[Tom Booth]

This is the right thread. I posted that video a few posts back.

I was going to try putting some kind of breather hole somewhere to relieve some of the pressure, but in an engine, good compression is normally what you want and introducing a "leak", though it might allow the engine to run, I thought would probably also reduce torque and power.

Cutting the piston down to a more reasonable size and reducing viscous "drag" by giving it a kind of RING, like an IC engine seems to have worked.

https://youtu.be/Opzd0yxWq98

My modification is pretty crude, but it worked anyway. Now the engine will run with any kind of (Non-Flammable) oil just fine. It also still runs on just graphite. Or even a mixture of both.

This engine still has at least one other major problem. The all metal displacer still conducts a tremendous amount of heat through to the cold end, which makes it harder to get it running in the first place.

A foamed glass displacer should help, and I might just cast the whole engine body out of ceramic.

Probably the oil would work even better if the piston and cylinder were made of metal, and with actual piston rings, like a real engine.

I'm finding out, mostly by experimenting and being skeptical and curious, that almost everything I ever knew about Stirling engines was wrong.

Like a Stirling engine can't run with oil on the piston. Probably an IC engine couldn't either if they had long tight fitting pistons with no rings.

An IC engine generally has pretty sloppy fitting pistons. Only the rings are just barely tight enough to make a good seal.

[Tom Booth]

The oil and a little graphite mixed together in that last video, reminded me of ferrofluid. Which reminds me of something else I wanted to try.

If a little magnet were put inside the glass piston, a ferrofluid "ring" would be a virtually perfect, frictionless seal.

[Tom Booth]

After going through another round of trying different timing settings, I found that the best overall performance seemed to be at slightly less than the standard 90° offset.

With just a little less advance, I think about maybe 88° the engine started up easier and faster, lit up the LED brighter, and could handle quite a bit of breaking without dimming the LED or stalling.

Recovery time after removing the break or reapplying heat was also faster.


https://youtu.be/D6F_cDjrEEU

However the bearings on this engine are not exactly precision so the slightly less than 90° advance may just be compensation for the sloppy bushings.

Anyway, seeing this model running so well with a Non-Flammable liquid lube. (I also really drenched the piston with lubricant this time, which I couldn't do before) it gets my confidence up that an IC to Ringbom conversion might be successful.

[Be OK]

q Tom Booth,Was thinking for the expensive helium,you could use nitrogen cheap and plenty. For the piston rub no idea what machines you have but i would grind 3/4 or more off the bottom, away so much that only 3 or 4 small lengthwise rills stand,would reduce friction much.

[Tom Booth]

Yes, any inert gas can be used, but helium is supposed to be the best in terms of power boost. Except hydrogen which is better than helium.

I like the idea of using hydrogen. Adds more power than anything else and can be made for free, well, not free exactly, but on a DIY basis from water

Lengthwise rills on the piston sound good.

In a Ringbom conversion, I'd probably just use the existing engine with the piston and rings it came with.

In working on engines in a repair shop, I always marveled when someone brought in some real old cast iron engine. The cylinders were always pristine. No scratches or scaring. Almost no drag, compared with any newer engine.

[staska]

Mine two cents. For air engine, we need not only air, but also a kind of air preparation system. At lest dryer. So - put after dryer, deoxygenator of any kind. Ordinary steel sponge heated to 800 degree or like will do the trick.

And working with nitrogen and some other gases - is totally safe with lubricants.

Or - if you limit yourself on 4-5 bar and your engine have mediocre compression aka correct phase angle for your 500 celsius source - it will not reach self ignition temperature.

[Tom Booth]

Mine two cents. For air engine, we need not only air, but also a kind of air preparation system. At lest dryer. So - put after dryer, deoxygenator of any kind. Ordinary steel sponge heated to 800 degree or like will do the trick.

And working with nitrogen and some other gases - is totally safe with lubricants.

Or - if you limit yourself on 4-5 bar and your engine have mediocre compression aka correct phase angle for your 500 celsius source - it will not reach self ignition temperature.

While all that is basically true, I don't really think it is necessarily desirable. Limiting the engine to "mediocre compression" and "correct" phase angle.

Most Stirling engines are fixed at a 90° advance. I think that this allows the engine to start relatively easy and run alright without any load, but that's about all.

Any automotive mechanic knows that a car engine with the timing (phase angle) even slightly off, for example, from a badly worn timing chain, runs like a dog, if at all. No power on hills poor acceleration, stalling, knocking, backfiring etc

Or timing can be off due to something as minor as the point gap being off by some few thousandth of an inch.

"Playing with the timing" on model Stirling engines has, I think, demonstrated, to me anyway, that adjusting the timing off of the "correct" position can result in much higher output, generally along with higher compression and more difficulty starting, but that is precisely why cars have vacuum controlled timing or computer controlled timing. The timing starts out in one position for easy start, then adjusts for running and according to speed and load so there is power accelerating and on hills etc. The timing is in constant flux adjusting to the circumstance

The other points, while true, make manufacture and operation more complicated and expensive.

Having the engine air tight and filled with some special gas, needing "dry" air and so forth.

A non-flammable lubricant would go a long way towards reducing the need for all that complication and added expense. Just take a regular engine and add a cheap, easy to make displacer can. Convert it to Ringbom.

[creast]

Hi,
I am new to this forum but have built two Stirling engines and now on my third which is a Rider Ericsson pumping engine at 1/8th scale.
The engine does run, sometimes for a few minutes and slows and can sometimes run out of control depending on the displacer position and heat input.
That is a problem I am working on but one thing that concerns me is lubrication, hence why I am posting here.
The displacer rod is drill rod ( silver steel in UK) running in brass and the power piston is aluminium running in stainless liner.
I know all the problems associated with lubricants, i.e explosions, gumming, drag etc but what did the original working full size engines do for lubrication??
I mean, way back in late 1800's early 1900's what did they use?? Apparently these engines ran for years.
Rich

[Tom Booth]

This is interesting and kind of amusing about how the pistons on the Caloric ship Ericsson were lubricated:

. The piston in the working cylinder is made six feet deep from top to bottom, concave underneath to fit the cylinder-bottom, and flat at the top. The top as well as the sides are of iron, but the space between is filled with gypsum and charcoal, non-conductors of heat. Thus while the bottom has the temperature of the hot air in the cylinder, the top is perfectly cool. The heat there is barely sufficient to keep the tallow used for lubrication in a fluid state, not to burn it. In fact one can stand upon it as it plays up and down, and many gentlemen amused themselves yesterday by riding there. This enables the engineer at any time to grease just the part of it which he may desire; when the ship is careening for instance, and the friction of the piston is all on one side, that side can be directly lubricated. This is a point of great practical importance, which cannot be attained in a steam engine. Nor is there any danger of burning the packing, for it is at the top of the piston, and never comes within less than six feet of the fire.

The cylinders act in pairs, and in each pair the action is reciprocating; that is to say, as the piston goes up in one, it goes down in the other.

http://hotairengines.org/open-cycle-eng ... tive-power

[Be OK]

Was a nice read Tom,but i assume that the rpm was low as the stand up the piston for fun :)

[skypupbob]

It was stated that it ran at 8 to 10 rpm, so yes very slow.
Tom, have you looked into air gun oil ? If the oil ignights in the gun, it will cause 'dieseling' which blows out the seals. So maybe it has a high flash point compared to normal oils? Just a thought.

[Tom Booth]

It was stated that it ran at 8 to 10 rpm, so yes very slow.
Tom, have you looked into air gun oil ? If the oil ignights in the gun, it will cause 'dieseling' which blows out the seals. So maybe it has a high flash point compared to normal oils? Just a thought.

I've tried two types of "non-flammable" gun oil, (not air gun, but regular firearm). They both were too thick and molases-like. One tended to foam up and turn white and watery? Like if an engine had been run with a lot of water in the crankcase.

Honestly, the best non-flammable lubricant I've tried so far was the Superzilla. But I found that it works best if the piston and cylinder are very thoroughly cleaned from any other residue of any kind of oil or graphite. The same company makes a gun lubricant: Gunzilla, but I haven't tried that yet.

I've also only been using a model engine with glass piston and cylinder.

I also found though, the liquid lube requires a slightly looser fitting piston. A very long snug fitting piston will run fine with graphite as the dry graphite has, I suppose, zero viscosity, but even the Superzilla, which is thin as water, still needs just a bit more room to flow, but there is a tremendous improvement in compression and torque.

The first time I tried the Superzilla there was still graphite on the piston and the engine bogged down, but that engine had a very long, super tight fitting piston

[Tom Booth]

Not exactly a speed demon but it ran (14 years ago)

https://youtu.be/wymijnR-oug

No mention of doing anything about potential explosion, changing the type of oil or anything.

[Tom Booth]

I had more or less settled on "Superzilla" as a potentially OK, but not great high temperature non-flammable Stirling engine lubricant.

This video/experiment, has me back on the quest for something better.

Something is smoking, and the clear glass cylinder is discolored, white/cloudy looking.


https://youtu.be/eGiJZzIkquA?t=327


I had tried some Superzilla on this engine previously, but thought I had cleaned most of it off. Apparently though, a puddle of it had formed around the displacer sleeve.

The stuff seems good up to a certain temperature, maybe somewhere between 500 to 1000°F.

It is still basically "non-flammable", but at very high temperatures maybe will boil off and turn gummy. (? Under certain circumstances).

When this engine began slowing down, though still getting plenty of heat, I shut off the heat to prevent any additional damage, not sure what was going on.

After cooling down, the engine would no longer operate on just hot water. It, infact, would hardly turn over manually.

On further inspection, I found that the piston and cylinder were coated with a white gummy substance which was binding up the engine.

Once I had that cleaned off the engine ran well again on just hot (120°F) water.

Previously, I found that silicone, especially if not fully cured, will cook, bubble, boil and expand and also does not play well with superzilla, causing the demise of my foamed glass displacer in another high temperature experiment.

On this LTD style engine, I DID use a thin smear of ordinary kitchen and bath silicone on the edge of the glass displacer housing engine body to help hold the silicon gaskets in place so the engine could be assembled.

The verdict is not in I guess, as far as what caused the engine to partly seize up with some white gummy substance. The not fully cured silicone, the Superzilla or possibly some chemical reaction between the two when the silicone is not fully cured (and when both are heated)

The problem may simply be the result of my impatience, not giving the silicone adequate time to fully cure before firing up the engine.

Anyway it's something I'll be keeping my eye on and watching out for.

At this point I suspect it is some interaction between the uncured silicon fumes and the residual Superzilla lubricant.

The silicon gaskets made from oven mats seem to be holding out, as far as maintaining a good seal, but otherwise appear to have virtually burned away.

At a minimum I've got at least two problems. Finding a High temperature non-flammable lubricant, and now also, a more resilient high temperature gaskets cement, gasket glue, or just gasket material.

Or, maybe I just need to learn more patience and give the silicon more time to fully cure, or avoid using Superzilla where silicone is also present.

Maybe I will do some experiments to see if there is some chemical reaction between silicone and the water based lubricant.

I had a similar problem before, when I used RTV red silicone as displacer glue and Superzilla as cylinder lubricant. The Superzilla turned to a frothy white foam.

Later on, though, after the silicone had cured I tried the Superzilla again and it seemed to work just fine.

As far as I can tell at this point it is the fumes from curing silicon reacting with the lubricant in some way.

Whatever the white gummy substance was on the cylinder, it did not do any permanent damage, but needed to be thoroughly cleaned off before the engine would run well again.