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There is a Japanese professor's YouTube channel which contains many lecture videos about Stirling engine:
https://www.youtube.com/@user-yw7eo3no6m/videos

from basic crank design (Lesson 02):
https://youtu.be/IgU9nilT0rM

to solar Stirling engines(Lesson 05 - part5):
https://youtu.be/7Z6NUf8z9Uk

This professor's name is 戸田富士夫 ( Fujio Toda ).
He has been working on Stirling engine for a long time.
Some models made by him which are showed in the lecture videos dates back to 1991.

I consider this lecture highly valuable and it should have much more popularity.
Unfortunately, the language barrier prevented this precious resource from being accessed.
I will try to translate this course into English text and share it in this thread.
The first lecture I'm going to translate is about a 100 Watt model:
https://youtu.be/k-JfSeiuU68

My ultimate goal is to help developing a open sourced Stirling engine plan which has detailed instruction.
The plan can be used by average machine shops to manufacture functioning engines with 100 Watt power or more.
I want a Stirling engine of this level but can't do machining.

If you know Japanese and are interested in this course, please visit this channel and give some comments to that professor.

Lesson 5 - 1 100Watt experimental Stirling engine: part A

It starts from 3:03 to 9:24 of this video:
https://youtu.be/k-JfSeiuU68?t=183

[translation starts here:]
This lesson will be separated into many parts.

Here we are talking about how to make Stirling engine into a practical thing.
First there are educational models( red sphere on bottom left of the screen ), which have been discussed in previous lessons.
And following that is experimental models( green sphere on bottom right of the screen).
From experiments done on these models, practical engine models can be developed ( blue sphere on top).

The educational models discussed in previous lessons are mean to build up student's capability to imagine(to plan), make prototypes, and solve problems for this kind of engine.
From the basis of educational models, we are now focusing on experimental models.
When it comes to durability, from several minutes to hours of maximum operation time is acceptable for educational models.
But a experimental model must withstand up to several thousand hours. This is the baseline.

The most decisive difference between educational and experimental models is the usage of piston rings.
In most educational models you can use syringes and things go well.
But in order to achieve enough durability, piston rings are required in experimental models.
Advantage also comes with the piston rings, like reduction of friction and prevention of (working)gas leaking.
After solving problems in experimental models, a practical model can be made.

This development process includes two things: analysis and simulation.
Analysis means getting measurements and data from the models.
Simulation means building mathematical models and using methods like Simpson's rule.
(The professor also mentioned many other methods but I don't know these things due to my lack of knowledge, sorry! )
Analysis and simulation are both necessary, they can't work without each other.
Without data from analysis, a simulation model cannot be made.
Without any simulation, you will blindly make random changes on the prototype engine and get no meaningful data.

Why are we talking about this issue here?
Because those existing engines which are practical, like diesel and gasoline engines, they all had been through this process.
I've made many educational models in the factory in old days and I had enjoyed my time during that.
By thinking how to solve problems in these models, I know more about this type of engine and finally create something useful.
This process( enjoyment, thinking, knowing, creation) is my central belief, which is written in Kanji on the top right of the screen.
(Sou Chi Kou Raku === Sou means creation, Chi means Knowing, Kou means thinking, Raku means enjoyment).

Lesson 5 - 1 100Watt experimental Stirling engine: part B

It starts from 9:25 to 15:08 of this video:
https://youtu.be/k-JfSeiuU68?t=568

[Translation starts here]:
This is our first experimental model of Stirling engine.
(This picture only covered half of the system, there are another half on its right)

I had been working on gasoline and diesel engines before, these are usually measured in horsepower.
I had studied on a 10HP gasoline engine and manipulated many of its settings to get the best performance.
When it comes to diesel engines, I studied a 20 to 30 HP model.
After that, I also had my hands on a V8 diesel truck engine which has 360HP.

Due to this background, though the Stirling engines are usually measured by Watt, we build our first experimental engine with the mindset from the world of horsepower.
We did simple simulations and made this prototype which looks quite rough.
This is mostly derived from a diesel engine.
The piston which is hidden in the cylinder on the right of this picture are actually from that diesel engine.
We made cylinder liners for the cylinder and fixed with iron frame and bars.

For safety issues, we used a heavy and sturdy arm (painted black) to transfer its torque.
50mm shafts are used for the same reason.
There are two flywheels(30Kg each) installed on each shaft.
Since there are two shafts (one not shown in the picture). Four flywheels are used in total.

Though there are 120Kg of weight in the form of flywheel, it can easily set rotating by hand.
We thought this was good to go and ran test on it, but it failed.

We used a chain to link two shafts.

Though not visible in the picture, there are 4 piston rings in each cylinder: First ring, second ring, third ring, and then oil ring.
It's quite dangerous to use only one piston ring on gasoline and diesel engines.
Once the only ring breaks, the engine fails and cause lethal threat.
This is especially important in maritime motors.
We thought this ring setting would have least possibility of gas leakage.

We then made our second experimental model from a V-type compressor.
Including cylinders and pistons, most parts are derived from that compressor.
Sadly, it also failed.

Eventually, it took us three years to build up a working model.

Lesson 5 - 1 100Watt experimental Stirling engine: part C
This is a juicy part! It described a rare design of piston rings that prevents working gas leakage.

It starts from 15:09 and ends at 25:31 of this video:
https://youtu.be/k-JfSeiuU68?t=924

[Translation starts here]:
From the painful lessons learned from previous models, we finally recognized the importance of specialized piston rings.
Here's a drawing of internal combustion engine's piston ring.
(Picture at 15:09 ~~~ 16:55 )
(Picture title: The path of gas leakage in internal combustion engines)
(The flow of gas is visualized by black arrows)

Usually there is grease in cylinders for this type of engine.
On the contrary, Stirling engines cannot use regular grease.
Because the grease can enter the hot side and get carbonized and jam the regenerator.
This will gradually decrease efficiency of this engine.
Therefore, Stirling engine cylinders usually have no lubricating.

Additionally, piston rings in internal combustion engines have gaps.
(Depicted on the right side of the picture.)
This gap will be wide and allow gas leakage when the engine is not in working temperature.
Even equipped with multiple rings, this design will eventually cause severe loss of working gas in Stirling engines.

When we asked professionals in Stirling engines for advice, we found out that there are special piston rings that are suitable for Stirling engines.
(Picture at 16:56 ~~~ 19:27 )
(Picture title: Piston rings for Stirling engines )
(Texture of the rings: Teflon plus carbon)
(1 Plain ring No.1)
(2 Plain ring No.2)
(3 Inner ring)
(4 Tension ring)

We then started using this type of piston rings.
First there are two layers of plain rings on the outside.
On the inner side of plain rings there is one inner ring.
Two plain rings are no aligned to make sure their gaps do not connect with each other.(depicted on the bottom of this picture)
The inner ring, which also has its gap not connected to other gaps, prevents gas leakage through the insides of plain rings.
These rings are made from Teflon mixed with 10 percent of carbon.
Since this type of material don't have enough tension, a piston ring spring(tension ring) is used in the innermost to deliver tension to plain and inner rings.
This combined set of rings prevents working gas from leaking.

With this type of piston ring we made our first successful model of experimental Stirling engine.
(Picture at 19:28 ~~~ 25:35)
(Picture title: The boxer type experimental model Stirling engine)
(Model made in 1985)
(The first working Stirling engine model)
(Piston diameter X Stroke: 50 X 87.5 mm Stroke volume: 170 cm3)
(Maximum output generated at 3atm pressure: 80 Watt)

The output at 1 ATM is only 18 Watt.
The original design of this model used 3 sets of piston rings in each cylinder.
We used 40mm wide timing belt instead of chains to transfer power output.
The heat source is applied in the middle of this model with insulation.
The input is about 2KW.

In fact the engine was unable to work initially.
We then tried to reduce friction by reducing number of piston ring sets to one in each cylinder.
But the model still failed to start.
We switched our attention to the timing belt.
By reducing width of the belt to 1 mm, the test model started.
Me and my teammates got really excited and reported to our professor on the next day.
From that on, we kept working on reducing frictions inside this system.
The shafts/flywheels and linkages were remade and well greased.
On problem remained was the slide shaft which was connected to the piston.
The original design was a stainless steel bar fixed by a slide bearing.
We replaced them with parts that have higher stiffness.
The piston ring was modified several times later.

Lesson 5 - 1 100Watt experimental Stirling engine: part D

This part is more valuable than part C.
It illustrates the importance of piston ring design and how a good piston ring works when pressure changes.
Most of the DIY project I've found on the internet didn't focus on this part.
This might potentially be the key factor for a Stirling engine prototype to become efficient and reliable.

It starts from 25:37 and ends at 36:01 of this video:
https://youtu.be/k-JfSeiuU68?t=1537

[Translation starts here]:
About this engine's fuel combustion status.
(go back to the previous picture of piston ring set for Stirling engine)
Diesel engines and gasoline engines have different phases when it comes to fuel combustion/ignition.
Though the combustion happens at the same spot, there are drastic changes when it comes to pressure and temperature.
Stirling engines have the same phenomenon.
The pressure inside each cylinder will change in different phases.

Such pressure change will seriously affect the performance of the engine when abrasion powder/ wear debris from the cylinder ring are generated.
First let's look at the upper drawing.
When abrasion started, the plain ring labeled as "1" will have a gap between it and its contact interface on its top.
And when the chamber is in positive pressure, working gas will leak through a passage which is depicted by hollow arrows.
We added water in the chamber and run tests. The leakage was then confirmed.
This made us realized that this piston ring set design is still not good enough.

Thus we used a improved design, which is a one-way piston ring.
(picture starts at 27:38)
Its sectional view looks quite similar to previous one.
There are two layers of plain rings.(notation call it "piston ring")
We replaced the inner ring with a Notched Rubber Ring.
By using this rubber ring, we detected no water leakage during water test.
A tension ring is used to hold other three rings in place.

Here's a detailed drawing of the notched rubber ring.
(picture starts at 28:27)
I will explain why and how these notches do in the following part.

This is the parts used to form a one-way piston ring.
(picture starts at 29:12)
(Two black plain ring on top, one notched rubber ring on bottom left, and one tension ring on bottom right.)
These are not made by me but ordered from Rikken(株式会社リケン, a Japanese company making engine parts)
There are three major supplier of piston rings and we choose Rikken for this project.
The piston rings ordered from Rikken worked far better than rings made by ourselves.
I still don't understand how but their product fits perfectly to our prototype piston.
Maybe it is because their product have much better precision.

Now lets take another view at the cylinder.
(Picture starts at 31:58)
(Picture title: one-way piston ring's structure)
(The piston is at the center of this drawing, there are a connecting axle on its left.)
(Two plain rings in black color is at the center's outer rim of the piston)
(A notched rubber ring in white/blue is under the plain rings)
(The tension ring is beneath all of them)

In order to show how this ring set works, let's move to next drawing:
(Picture starts at 32:33)
(Picture title: mechanism of action( situation: Positive pressure inside cylinder) )
Pressure P1 is higher than pressure P2.
This happens when the piston is compressing the working gas.
A stream of gas flow will show up(depicted as red lines and arrows)
Since there are notches on the rubber ring, a branch of the flow will go through and apply pressure to the innermost side of the ring set.
This branch flow is noted as "Pi" in the picture.
It will further tighten the ring set against the cylinder wall and prevent working gas from leaking.


And then when the piston goes to the opposite direction, things changed.
(Picture starts at 34:06)
(Picture title: mechanism of action ( situation: Negative pressure inside cylinder ) )
Pressure P2 is higher than pressure P1.
And you can see those two plain rings are pushed to the opposite side of the groove.
The notches on rubber ring are now covered by plain rings.
So the air outside cannot go through the rubber ring.
Instead, the pressure is weakening/neutralizing the force from the tension ring.
If the tension ring is not strong enough, the air will break through the connecting face between plain rings and the cylinder wall.
(depicted as the red arrow on top)

From then on the Stirling engines done by me are using this type of piston ring.

Lesson 5 - 1 100Watt experimental Stirling engine: part E

This part provides some test results to proof that the one-way piston ring is better.
This allow the prototype to get significantly closer to theoretical performance.

They also tried using a buffer pressure to boost engine performance by applying it on the whole system.
This created positive results(Which is similar to the effect of one-way piston ring).

It starts from 36:02 and ends at of this video:
https://youtu.be/k-JfSeiuU68?t=2162

We investigated the pressure patterns of piston cylinders using different types of cylinder rings.
(Picture starts at 36:02)
(Picture title: Regular piston rings versus one-way rings, Comparison 1)
The green line is the pressure changes of piston with regular rings.
Apparently it is much lower than the theoretical pressure.
The leakage caused significant loose of efficiency.

The red line is data from one-way piston rings.
Its lowest pressure is much closer to 1 atm(100 kPa).
This curve is much more symmetrical and its duration of positive pressure has less difference to negative pressure.
As you can see, it is much similar to the blue line(Theoretical value which has no leakage).
By using one-way piston rings, the average pressure is around 120 kPa.
It has much higher output compared to regular piston rings.

Let's first take a look at P-V diagram of these two type of piston ring's data.
(Picture starts at 37:52)
(Picture title: Regular piston rings versus one-way rings, Comparison 2)
The green loops are from regular piston rings and red loops are from one-way piston rings.
The larger and rounder (fat) loops are in expansion phase.
The thinner loops are in compression phase.
As you can see, the red loops covers wider range of pressure difference.
This pressure difference means indicated work.
When the engine starts running, it will become indicated power/horsepower.

And here's the indicated power data.
(Picture starts at 38:28)
(Picture title: Regular piston rings versus one-way rings, Comparison 3)
There are three pairs of data.
Each pair contains one data curve from regular rings and one from one-way rings.
The lowest pair is shaft output ( brake power).
The middle one is indicated power.
The top one is Torque.
When it comes to brake power, the regular type can only reach 20Watt, but the one-way rings can reach up to 30 Watts.

In the case of indicated power, the difference is more apparent.
The one-way rings can generate 30Watt more than regular rings.
This situation is consistent to the torque data.
If you can maintain higher pressure differences, you will get better output.

Now let's go back to the experimental model itself.
(Picture starts at 39:48)
(Picture title: Small scale experimental Stirling engine(Buffered pressure type) )
We applied buffered pressure to the experimental models.
The buffered pressure is 2.5 atm.
Usually it's fine to keep such pressure.

But for the sake of safety, 1.2Kw heat supply is used.(I don't quite get it since the speaker's voice turned into whisper)

The two piston cylinders are sealed in buffer casings and ducts are connected to the buffer pressure tank.
On the left of this picture, there's a metallic arch which contains equipment's that measure mechanical output.
On the center of this picture, a bottle shaped device is installed to measure engine pressure.
There is a device for adjusting heating on the bottom right of this picture(A black and barrel-like thing on the ground).

With buffered pressure, we can further investigate this model in different setting.
(!!! In this setting, the one-way piston ring is not used in both 1atm and 2.5atm groups!!!)
(Picture starts at 40:40)
(Picture title: RPM(Rotation per minute) versus gas temperatures on each part of the engine).
Data in 101.3 kPa(about 1 atm) is presented by red squares and 250kPa is presented by blue circles.

The Tc means the gas temperature at the cold end of the engine.
Both group end up at about 40~50 degrees Celsius.

TRH and TRC are temperatures measured at regenerator.
TRH is close to Hot side, TRC is close to the cold side.
The 101.3kPa group reached 600C on TRH and 100C on TRC.

(This graph was not further explained by the speaker)

This is the engine performance under buffered pressure.
(Picture starts at 41:40)
(Picture title: Engine performance under different buffer pressure)
When applied with 250 kPa buffer pressure, the test model generates almost doubled amount of shaft power.
Though this is still a experimental model, we wanted to get more indicated power(Higher than 100Watt).
Thus we tried some methods to push the output even higher.
Let's look at the indicated power at the middle of this graph.
In the case of 101.3kPa, the power increased linearly with engine speed.
This means the 1.2Kilo Watt heat source is enough for this setting and can go up to 100~110W indicated power.
But in the 250kPa group, the power/rpm relationship became non-linear beyond 600 RPM.
It means the heat source is not strong enough.
We took the risk and increased the heat source to its maximum: 2KWatt.
After this adjustment, the indicated power/rpm relationship in 250kPa group became perfectly linear(not shown in this graph).
The goal for going beyond 100Watt is achieved, but the protective sheath and other things around the heater got burned.
Therefore we had no choice but to stop the experiment.

gitPharm01,

Thank you for all of the work you are putting in here. It is a lot to digest and personally I have not yet given it the time it deserves. This type of real world experimentation is exactly what this community needs right now. Keep it up!

VincentG wrote: ↑Thu Mar 23, 2023 6:41 pm gitPharm01,

Thank you for all of the work you are putting in here. It is a lot to digest and personally I have not yet given it the time it deserves. This type of real world experimentation is exactly what this community needs right now. Keep it up!

Thanks for the comment!
This is all I can do since I am not able to do machining or casting.
These resources and data from Japan dates back to 1980's and I am afraid that they might be lost forever.

I've found a Japanese company which is based on Stirling engine technology and it somehow survived until today.
I will use another post to introduce this company later

Just had a full read. Thats quite an amazing design for the piston ring! And an impressive performance boost to go with it. I think it would lend itself well to a more developed Stirling engine.

Is it possible to translate the part about what looks to be an LTD engine on that cart?

VincentG wrote: ↑Fri Mar 24, 2023 3:49 pm Just had a full read. Thats quite an amazing design for the piston ring! And an impressive performance boost to go with it. I think it would lend itself well to a more developed Stirling engine.

Is it possible to translate the part about what looks to be an LTD engine on that cart?

If you mean that solar Stirling engine shows up on 55:14 of the video, then yes I will cover it.
There is a lens on top of it to gather solar heat.

I've translated this video from 00:00 to 43:58.
This part might be in part G or H.

Lesson 5 - 1 100Watt experimental Stirling engine: part F

This part talks more about gas leakage both in piston and the shaft seal(Which is used in buffer pressure test in part E).
They developed a one-way shaft seal to prevent leakage and frictional loss.

It starts from 43:58 and ends at 53:05 of this video:
https://youtu.be/k-JfSeiuU68?t=2638

The next thing we did was a gas leakage test.
(Picture starts at 43:58)
(Picture title: Test device for gas leakage)
With this setting in the picture, we measured gas leakage in three cases:
1.piston with regular piston rings.
2.piston with one-way piston rings(both the old design in part C and new design described in part D)
3.A syringe(injector) piston which is used in educational Stirling engine models.

The test result was presented in the form of Equivalent Diameter (in mm)
(Picture starts at 44:38)
(Picture title: (piston)Sealing devices and their equivalent diameters)
The regular type engine rings got highest value of equivalent diameter(0.35mm, a huge one).
The original one-way piston ring significantly lowered the value.
The new one-way piston ring further improved leakage problem.

However, the injector piston has the lowest leakage.
(Educational models usually use this type of piston and though they have much lower heat input,
such low friction and leakage prevented them from suffering problems we face in models with metallic pistons)

And then let us talk about the shaft seals.
(Picture starts at: 46:27 )
(Picture title: The structure of one-way shaft seals)
We tested applying buffer pressure on the engine.
But there must be a seal layer(partially depicted in gray in this drawing) to hold such pressure.
And rotary shaft of the engine must go through that seal.
So a seal ring must be applied to this seal to prevent pressure leakage.
On its right, there is Buffer pressure sealed in the cavity of the seal.
On its left is atmospheric pressure.
We used our new one-way piston ring initially.

And then we developed a new type of shaft seal:
(Picture starts at 47:27)
(Picture title: the one-way shaft seal)
The key is a layer of rubber ring holding other rings together.
It has a special shape.(Like a F but the lower horizontal stroke of that "F" stretches downwards)
First it holds two seal rings together.
On the opposite side there is a tension ring applying force to the seal ring.
The rubber can cover most of the possible leakage points and hold buffer pressure on the right of this drawing.
The only possible leakage is from the deformation of that shaft.

We also tested other existing types of shaft seals.
(Picture started at 48:32)
(Picture title: Discussion on shaft seals)
(On the left: Oil seal. On the right: mechanical seal)
In the case of oil seal, a spring is used to apply pressure on the seal loop and make sure the loop seals the shaft.
The seal loop is made from different types of rubber for different types of gases.

Another type is mechanical seal.
It is used when no gas leakage can be tolerated.
This type is usually for rotating shafts.

This is the frictional loss(of power) on each type of shaft seals.
(Picture started at 50:07 )
(Picture title: frictional loss from shaft seals )
(The loss is measured in Watt against rotational speed of the shaft)
The new type on-way shaft seals managed to out perform other seals.
The worst case is nitrile rubber seals.
Teflon seals performs much better.

Here's some test data from Rikken company(The manufacturer of one-way piston rings)
(Picture started at 52:12)
(Picture title: working gas and the loss of sealing materials)
This set of data is about the frictional loss of sealing materials when the sealed shaft is rotating in different speed with different working gas.
(!!!The experimental platform that generated this data set is not that Stirling prototype model we've been talking about so far!!!)

There are three parameters included:
1.Quantity of loss of sealing materials (in u/100Km) in Z axis
2.working gas type( Air, nitrogen, helium, hydrogen) in X axis
3 relative speed of friction( in ) in Y axis
(The sealing material in this data set was not mentioned)

The air group has no doubt suffered the most serious loss.
Nitrogen and Helium group have much better result
The hydrogen group has the best performance.

Since the air group has the risk of high frictional loss and will cause leakage eventually, we used one-way shaft seals to evade this problem.
(Our goal is to make a Stirling engine which is working in plain air,not sealing the whole system,including flywheels and crank shafts, in special gas.)

Lesson 5 - 1 100Watt experimental Stirling engine: part G

This is the final part of this video.
This part served as a teaser which discloses footage of Stirling engine models that will show up in subsequent lessons.
The incinerator powered model in 59:53 is quite attractive to me and its blueprints and operational footage is a valuable resource.

Lesson 5-2 will continue on talking about 100Watt experimental Stirling engine and this time there will be more detailed blueprints and specs of this model.
https://youtu.be/k-JfSeiuU68?t=3190

[Translation starts here:]
Following this lesson(5-1), there will be 5-2,5-3,5-4 and so on.

(Picture starts at 53:09)
(Picture title: experimental engine 1)
In the following series, engine models like this will be discussed.
(Video clip started with loud engine noise and the speaker's voice was unrecognizable)

(Picture starts at 54:27)
(Picture title: experimental engine 2)
(Picture description: Solar engine(made in 1995),
This is a LTD Stirling engine powered by concentrated solar heat.
It delivers 2 Watts of power )
This model uses a parabolic reflector to attract solar heat.
It could only reach as high as 100C Celsius.
I will talk about this in Lesson 5-5.

(Picture starts at 55:23)
(Picture title: experimental engine 3)
(Picture description: 10Watt Stirling engine(made in 1991),
This is our first LTD Stirling engine. Heat source temperature is 130C,
A 3atm buffer pressure is applied and it delivers 13 Watts of power )
This is a 10Watt class, low temperature difference Stirling engine.
The shape is rectangular.
Displaces inside this rectangular cavity can be lifted(and lowered).
Power piston used in this model has 300mm diameter and its parts are ordered from Rikken company.
It has two flywheels(1 meter in diameter, 20mm thick).
This model took us a lot of work to build.
I will talk about this model and the data generated from it.

(Picture starts at 56:43)
(Picture title: experimental engine 4)
(Picture description: Exhaust heat powered Stirling engine(made in 1994),
This is a hybrid system combining Stirling engine with a gasoline engine.
3 percent(heat energy) of the exhaust from gasoline engine was extracted)
The bright yellow machine is a gasoline engine.
The combustion temperature can go as high as 3000C and its exhaust is about 900~800C.
There are still some energy in the exhaust and we wanted to try harvesting it, thus this system was built.
I will talk about it later in Lesson 5-4

(Picture starts at 57:36)
(Picture title: experimental engine 5)
(Picture description:Alpha Stirling engine using hot water as heat source(made in 1997),
In order to minimize the engine size while maximizing its output,
we tried Alpha type design in a LTD Stirling engine for the first time.)
Before this model, we've built all our LTD engines with Gamma type design.
You can see some green(cold) and black(hot) pipelines and water are flowing through them.
The metallic block in the middle contains the regenerator this engine.
On top of this block is the expansion side and the compression side is beneath of the block.
I will talk about this model and the data generated from it.

(Picture starts at 58:31)
(Picture title: experimental engine 6)
(Picture description: Small-sized universal Stirling engine(made in 1992),
It's powered by electric heat coil.
With a 6atm buffer pressure, it reached 100Watt output )
This is actually the same engine from "experimental engine 1".
It was buffered with a 6atm pressure to boost its output.
This is yet another model I will talk about.

(Picture starts at 58:55)
(Picture title: experimental engine 7)
There are several models in this picture.
On the left there is the solar LTD Stirling engine.
Its flywheel was removed.
In the middle sits the 10Watt Stirling engine, which also had its flywheel removed.
Though not quite visible in the picture,
there is one engine sitting between the table and 10Watt model.
This is the exhaust-heat-powered engine from "experimental engine 4".
It was removed from the main frame.
The white plate covered by a transparent dome is actually a educational Stirling engine model.

(Picture starts at 59:53)
(Picture title: experimental engine 8, 100Watt class, biomass powered)
(A detailed blueprint with materials listed in the table on the right)
Here's a model powered by an incinerator(焼却炉, small-sized incinerators are common in Japan for burning garden wastes).
The cold side is cooled by water, and the warm water can serve as bathwater.
It's a 8-cylinder design.
(Picture starts at 1:00:26 )
(Picture title: experimental engine 9, 100Watt class, biomass powered(working under atmospheric pressure))
This is the assembled engine.
Its parts are illustrated in a smaller picture on the right.
regrettably, I was not skilled enough to make them myself and these are ordered from professional machine shops.
There are 8 black cylinders on its top.
They will be heated by the flame in incinerator.
In order to reach 100Watt output, the system must be sealed and applied with a buffer pressure.

Here's how it moves:
(Video clip started at: 1:01:30)
(title: experimental engine 10)
You can see 8 white cylinders moving.
These are made from light-weight ceramics.
The whole system is made from high precision parts and thus the movement was quite smooth.

And here's how it works with heat input:
(Video clip started at : 1:02:00 )
(title: experimental engine 11)
Note there's only 4 cylinders installed in this test run.
The output was only 10 to 20 Watts.
It can reach 600 rpm.
Temperature of the heater is 727C.(Not actual temperature on the hot side)
This test run created much lower output(since it has only half of the cylinder working and no buffer pressure)
We just wanted to make sure its mechanism can run as smooth as designed.

And here's the last one.
(Video clip started at : 1:03:03 )
(title: experimental engine 12, 100Watt class Lower Thermal difference Stirling engine)
The LTD models we've built usually has only about 10 Watt output.
But this one reached 100Watt.
This model was built before year 2000.
130C hot water will flow in and cold water is used to cool engine's hot side.
The temperature difference is about 100C.
The power piston in this model is 400mm in diameter.
Its fly wheel is 1meter in diameter and 20mm in thickness.
The displacer's diameter is 800 mm.
This thing runs at 200 rpm.
I also would like to discuss this engine in later chapters.

This is the end of Lesson 5-1 and let us meet in lesson 5-2.

Lesson 5 - 2 100Watt experimental Stirling engine: part A

This video follows the 5-1 and takes a closer look at a 100Watt class Stirling engine.
After several times of modification, its thermal efficiency is close to Carnot efficiency!!

This part starts from 0:00 to 3:52
https://youtu.be/9Risg8ItEjo

[Translation starts here]:
Greetings everyone, we are in Lesson 5-2 of the "Introduction to Stirling engines" course.
In this lesson, we will further discuss on a 100W class, small-sized Stirling engine.

But first let's see a diagram of my team's first successful experimental model, which was mentioned in Lesson 5-1.
In 5-1 there were only photos of this horizontally opposed Stirling engine.
(Picture starts at 0:39)
(Picture title: 100W class Horizontally opposed Stirling engine)
{
notation on this picture: 1 Expansion piston5 Heater9 Timing belt 2 Compression piston6 Regenerator10 Flywheel 3 Piston ring7 Cooler11 Cylinder liner(compression side) 4 Heat-insulating cap8 Sheathed thermocouple12 Cylinder liner(Expansion side) Table contents: stroke volumeExpansion chamber170cm3 (Inner diameter x Stroke ) 50 x 87.5 Compression chamber137cm3 (Inner diameter x Stroke ) 50 x 70 Heat exchangerHeaterDiameter 2mm Length 50mm RegeneratorBrass-made metallic mesh CoolerDiameter 2 mm Length 80mm }

On the left there is a expansion piston labeled as "1".
On the opposite side is compression piston labeled as "2".
Between them there are heat exchange mechanisms, including heater, cooler, and regenerator.
Note that slide shafts which are connected to flywheels by a crank arm.
They are stabilized/fixed by slide bearings.
A timing belt links two fly wheels.
This layout is much easier to debug and adjust.
There are two sets of one-way piston rings in total.(Labeled as "3").
In the case of buffer pressure, a one-way shaft seal is applied near each slide bearings.

This experimental modeled had generated many meaningful data and helped us understand how to build practical Stirling engines.
But a length more than one meter is too large for a 100W generator.
In order to get a compact size, we turned the direction of shafts to vertical and reduced flywheel count to one.
All other parameters remain the same.(Which is describe in the table)

Lesson 5 - 2 100Watt experimental Stirling engine: part B

A compact Stirling engine is discussed in this part.
The professor showed the real parts of this model and how they are assembled.
He forgot to switch the screen to full-screen at that part so you have to look at the bottom right.

This part starts from 3:52 to 14:11
https://youtu.be/9Risg8ItEjo?t=232
(Picture started at 3:52)
(Picture title: 100W Class Vertical type engine)
This model includes a regenerator, which is now shown in this drawing.
(It is on top of the two cylinders)
Through this transformation, we shrink the model in previous part in to a compact build:
304 *462 * 136 mm.

We did a lot of calculation for building this model.
Schmidt cycle, flow loss in regenerator, friction, heat loss during transfer and other aspects were considered during calculation.
After this process, this model was then created.
About calculation, since a lot of jargon will show up in the following discussion, I will explain them in later videos.

(Back to the model's drawing)
(On the right sight of this drawing, frontal view of this model)
On its left is compression piston.
The one-way piston ring is used in this case.
And this is a model of it.
(Starts from5:57,
Please look at the bottom right of the screen,
the professor is holding a transparent piston cylinder )
It is easy to pull the piston out, since it still let a trace amount of air in.
But it requires a lot of force to push this piston back.
This is how one-way piston rings works.
In this case the gas inside this transparent cylinder cannot escape and caused huge resistance.

(The professor swapped to another item(a metallic cylinder) at 7:13)
When it comes to structure, this is part of the expansion piston.
On one side it is connected to the shaft and it will move in cylinder in axial direction.
There are two rings on the piston.
(On professor's hand at7:31)
This is that Teflon ring with 10% Carbon.
On its inner side, a notched rubber ring is used.
(On professor's right hand at 8:10)
This is the key for one-way piston rings to work.
And finally there is a tension ring at the innermost position.
(At 8:22. The professor shaken the cylinder with plain ring and rubber ring removed,
Some noise was made by it)
This is noise made by the tension ring.

The rubber ring is installed on this ring.
(At 8:36, The professor put the rubber ring back.)
And then the plain ring should stack on it.
(At 9:00, The professor re-installed the plain ring.)
I only installed one, there should be two in one functional piston ring set.
The gap of each plain ring should not be at the same position.
This how the one-way piston rings look and work.

And the piston is connected to a sliding shaft.
(At 9:19, The professor held one metal bar with both of his hands)
This shaft has been treated with nitridation to harden its surface.
Since it's hardened, it became more resistant to abrasion.
However, two ends of this shaft were not treated.
You can see some scratches on this side.
This is caused by a grinder.
If the hardened surface were put under the grinder, it would be the grinder to get scratched.

Here's a slide bearing.
(At 10:38, The bearing is on his left hand)
The shaft is inserted into the bearing like this.
And then these connected parts are installed on the engine.

Here's the engine's cylinder.
(At 10:52, on his left hand)
This is made from one metal block.
Its inner diameter is 50mm.
And the other side has this set of holes.
This is for back-pressure.
(At 11:15, he flipped the cylinder to show another side)
There are two flanges on this cylinder.
And one o-ring is put on this end to prevent gas leakage.
(At 11:34, he is pointing that area with his left hand)
And then this cylinder can be install to the mainframe like this.
(At 11:40, he simulated the installation of the cylinder)

By repeating this process described above, two sets of cylinders and pistons are completed.

It was quite difficult to design this engine.
Many aspects, like friction, must be considered.
For example, this is a shaft seal.
(At 12:57, a black ring on his left hand.
He then put this ring on the tip of the shaft.
This was quite tight and could not fit in)
And here's another seal, which is not for this shaft.
(At 13:25, This one obviously is too large)
We tried parts with many different materials.
Eventually, we used one-way shaft seal like this.
(At 13:40, A white/transparent ring on his left hand)
This one is not very visible on the camera.
We tried this thing and found out that this creates lowest friction.
Thus this design is implemented.
The shaft seal is installed here.
(At 14:06. On the left half of this drawing. He pointed with a red dot near the center of the flywheel )