toy alpha engine

Discussion on Stirling or "hot air" engines (all types)
cbstirling2
Posts: 120
Joined: Sat Dec 17, 2016 9:35 pm

toy alpha engine

Postby cbstirling2 » Mon Feb 06, 2017 10:55 am

I saw this engine on ebay, but it sold out too quick.
It is stated to be an alpha engine. (It could be but from the picture it is hard to confirm.)
It is stated that the generator will produce up to 5 volts.

Could the performance be improved (noticeably) with a simple regenerator plumbed into the rubber hose? If so, what design?
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CBStirling2

Ian S C
Posts: 1984
Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: toy alpha engine

Postby Ian S C » Tue Feb 07, 2017 2:12 am

I'd tend to modify the hot end if I wanted more power. First change the hot cap for a stainless steel one, then investigate the construction of the Heylandt Crown on the hot piton, it should be a hollow item , made of stainless(best), or mild steel, light weight and without leaks. A bit of thought might have to go into the design of a regenerator, it may not be of great importance, but worth trying. It could possibly do with more effective cooling fins. If you are experimenting with the power out put, it is good to be able to change the size of the pulley, and you might find that changing the size and weight of the fly wheel.
Ian S C

cbstirling2
Posts: 120
Joined: Sat Dec 17, 2016 9:35 pm

Re: toy alpha engine

Postby cbstirling2 » Fri Feb 24, 2017 8:40 pm

I got this in the mail today and started it up. I'm very amazed about how much power it has.
Comparing this to my 2 gamma engines, Alpha engines are very noticeably superior. It is no wonder that Andy Ross devotes almost all his time to Alpha engines.
CBStirling2

cbstirling2
Posts: 120
Joined: Sat Dec 17, 2016 9:35 pm

Re: toy alpha engine

Postby cbstirling2 » Fri Feb 24, 2017 8:44 pm

Ian, thank you for your response above. the cylinders might be the best way to increase power , it'd be a drastic change to the engine plus I' lack a lathe. Two things seem to be a simple change to the engine, one is adding cooling fans and the other is addition of a regenerator. 3rd change that I could do without a lathe is to change the phase angle by moving the cooling piston, Andy Ross hints that has interesting effects on the power.
CBStirling2

Ian S C
Posts: 1984
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Location: New Zealand

Re: toy alpha engine

Postby Ian S C » Sun Feb 26, 2017 12:56 am

I'm not sure how it could be done with that lay out, but fan cooling is very effective.
Ian S C

cbstirling2
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Re: toy alpha engine

Postby cbstirling2 » Sun Feb 26, 2017 6:17 pm

Unlike my gamma engines, the hot and and the cold cylinder are almost perfectly thermally isolated. After I ran this Alpha engine on two tanks of alcohol the cold side was still not hot to touch.
CBStirling2

Ian S C
Posts: 1984
Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: toy alpha engine

Postby Ian S C » Mon Feb 27, 2017 12:36 am

That's good to hear about the lack of heat transfer. The one thing you could try to improve the out put from the generator is to change the generator, but that relies on you having a collection of motors suitable, I have but that's no use to you. The motor should be one that revs a a fairly low speed, most of the little motors are high revving, and to get a voltage out similar to the rated voltage in for the motor you have to spin it up to the same or slightly faster. Using the same motor as you have, the change could be tried of changing the size of the pulley. Make the big one bigger, the generator will go faster,b the votage goes up but the actual power/current output will go down, and the opposite if you make it smaller.
Ian S C

cbstirling2
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Joined: Sat Dec 17, 2016 9:35 pm

Re: toy alpha engine

Postby cbstirling2 » Tue Feb 28, 2017 10:47 pm

Ian,
Someone else recommended using a resistor to be the load on the generator to get more accurate readings of power.
I ordered a tachometer on Amazon, only 12usd. Amazing how inexpensive.
As for a regenerator, I have a small brass tube, I plan to put that inline but have a vinyl tube jacket it for insulation.
My thought is the brass will pick up the heat from the air going back and forth. I will have it be connected by a short length of hose on each end so the brass is thermally insulated from the hot and cold cylinders as well.

Do you think a brass tube would be sufficient? Or should I try a bigger tube with wire inside?
I could solder a 3 tubes and roll carb screen and place it in the middle to increase internal surface area...

Thoughts?
CBStirling2

Ian S C
Posts: 1984
Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: toy alpha engine

Postby Ian S C » Thu Mar 02, 2017 1:26 am

It could be worth trying both brass and steel(steel brake line) tube, and compare it with the plastic tube.
Ian S C

cbstirling2
Posts: 120
Joined: Sat Dec 17, 2016 9:35 pm

Re: toy alpha engine

Postby cbstirling2 » Sat Mar 04, 2017 6:03 pm

My brother and I experimented with two regenerators that I made. We had a thermocouple on the cold cylinder, and a voltage meter and amp meter period we used a thousand on resistor as a loan from the generator.

First thing to mention it's very difficult to get only one variable change when testing because if you run the engine and then make the change it takes awhile for the engine to warm back up and the cold cylinder does gently warm over time. The most accurate way would be to actually do long runs with each different part recording data each minute with a sufficient cool down in between.

I used a 1000 ohm shunt resistor. Max voltage recorded across the resistor was 4v, with amp meter in series reading 4 milliamps.

Regenerator attempts: brass tubes 4.5 cm long covered by hose the whole distance with a hose only gap of a few millimeters on each end. As Ian said, steel would have been better but I was unable to find any scrap brake lines small enough. Volumetric heat capacity of Steel has better than brass from what I've been reading.

Regenerator tubes:
1/16 inch ID
3/32 ID
4.5 cm long
The tubes were attached with short hoses on each end with a larger hose covered the bare metal to act as insulation.

Interesting it appears that the larger diameter brass tube performs worse than the stock rubber hose. I think there is two possibilities for this one is the stock hose has about a unsweep volume of 174 millimeters cubed, on the larger brass tube has a volume of 188 millimeters cubed. Also the stock hose took a gentle curve from port to port, but I used to shorter hoses for the regenerator and it took more of a straight line so there's two bends and perhaps that cause turbulence for the air flow?

Smaller diameter brass tube - I'm not certain enough to say it didn't work, but it didn't seem to improve it either.

Our highest recorded voltage and amperage was with the stock hose but we need to practice more thorough testing procedures so it's hard to say what the true results were.

Thoughts?
CBStirling2

Ian S C
Posts: 1984
Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: toy alpha engine

Postby Ian S C » Sun Mar 05, 2017 1:23 am

Another thing you could try is to put fairly thin steel wire in the tube, don't pack it in too hard. Or you could try teasing out a metal pot scrubber(they are a bit coarser than steel wool), and threading that through the tube. After filling the tube either way, blow through it, there should be minimal resistance.
Ian S C

Trevor
Posts: 171
Joined: Sun Nov 06, 2016 4:07 am

Re: toy alpha engine

Postby Trevor » Sun Mar 05, 2017 2:30 am

Interesting idea of yours Ian - Using Stainless Steel coarse scourer in a small model seems to work better that a solid displacer. Some of the small models I have, have been converted to SS wool and I get better results. Also some small tape drive motors make excellent DC generators and will work under low RPM.

cbstirling2
Posts: 120
Joined: Sat Dec 17, 2016 9:35 pm

Re: toy alpha engine

Postby cbstirling2 » Sun Mar 05, 2017 4:55 am

I just realized that have small diameter stainless tubes - metal chopsticks!
They are slightly conical, so depending which chunk I use, I will have different diameters.
Do you think that a tube lacks sufficient surface area? (Trev post suggests so. Wife will be happier as chopsticks won't be cut up... )

I also have stainless pot scrubber. A concern here is that if the engine ingests the unsecured strips. Any idea on design to prevent that? Or is that of low risk? Mmm... If I cannot blow out wire, then the pistons won't ingest it, I suppose.
CBStirling2

Ian S C
Posts: 1984
Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: toy alpha engine

Postby Ian S C » Mon Mar 06, 2017 1:32 am

I think that if you put the pot scrubber material in the joining tube, the reduced diameter connecting tubes at each end will stop any movement, try it with the plastic tube, you will be able to see if there is any movement.
I didn't know that stainless chop sticks were hollow, one of the shops I visit in the city has them, I must look more closely at them next time I'm in town.
Ian S C

Trevor
Posts: 171
Joined: Sun Nov 06, 2016 4:07 am

Re: toy alpha engine

Postby Trevor » Mon Mar 06, 2017 3:20 am

Hi Guys - Ian is right CB and SS fine wool is a real problem as bits of it get into the seals and cause all sorts of problems, however, the coarse one does not and seems top hold together. I have ran my fan one for another 15 hr long run a couple of days ago and was not a problem. I was amazed at its performance and how the rubber diaphragm is holding together. Anyway that's my 2 bob's worth on the SS scourer.
Trev


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