Author Topic: Rocker V Stirling Engine  (Read 14088 times)

Offline Admiral_dk

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Re: Rocker V Stirling Engine
« Reply #60 on: April 03, 2018, 10:21:44 PM »
Wow - not only good looking design and execution, but it runs fast enough to produce real power, very good for a Sterling Engine - I'm officially impressed  :NotWorthy:

Best wishes

Per

Offline Craig DeShong

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Re: Rocker V Stirling Engine
« Reply #61 on: April 03, 2018, 10:26:32 PM »
Very nice, and it's not dancing around all over the table !
Craig

Offline Dave Otto

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Re: Rocker V Stirling Engine
« Reply #62 on: April 04, 2018, 12:28:39 AM »
Very nice Plani!

The speed is amazing, have you put a tach on it?


Dave

Offline Zephyrin

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Re: Rocker V Stirling Engine
« Reply #63 on: April 04, 2018, 08:59:53 AM »
Congratulations, great runner, and no vibrations!
According to the sound track, speed is 1740 rpm...nice results !

Offline Ian S C

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Re: Rocker V Stirling Engine
« Reply #64 on: April 04, 2018, 12:45:06 PM »
Plani, have you had a tacho on the motor, it sounds to me that its getting to 2000rpm at least, that's a very good motor.
When Andy Ross was producing kits for hot air engines he had a source stainless cups for displacers and hot caps.
The case of a C size NiCad battery is a similar size to the hot cap on this motor.  If anyone goes this way, be careful digging the inside  out of these things, and use a dead battery.  I don't know exactly what these battery cases are made of, but they seem to work ok.
Ian S C

Offline Plani

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Re: Rocker V Stirling Engine
« Reply #65 on: April 04, 2018, 05:29:56 PM »
Thanks everyone for the compliments!!! It is very much appreciated!  :cheers:

Perry, the hot cap as well as the displacer are deep drawn cups which are made for electronics housings. I don't know exactly where to get them, since I got mine from Andy Ross.

When making the video, I dinn't measure the speed of the engine. But I think Zephyrin is spot on.
I did take some measurements on another occasion thoug  ;D:



Plani
« Last Edit: April 14, 2018, 11:26:37 AM by Plani »

Offline tvoght

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Re: Rocker V Stirling Engine
« Reply #66 on: April 04, 2018, 07:01:36 PM »
I can only repeat what others have said about the beauty and smoothness of your engine, Plani. Bravo!


--Tim

Offline Art K

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Re: Rocker V Stirling Engine
« Reply #67 on: April 05, 2018, 02:58:15 AM »
Plani,
Ditto on what everyone else is saying. It runs great.
Art
"The beautiful thing about learning is that no one can take it away from you" B.B. King

Offline Plani

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Re: Rocker V Stirling Engine
« Reply #68 on: July 07, 2018, 08:47:00 PM »
Oh wow, time is really going fast!
Anyway, today I got finally around to measure the Power of the little Stirling.
But before that, two little modifications had to be done: The engine got a heat deflector, to keep the radiant heat from the flame better away from the engine block. And then the lantern type wick of the alcohol burner was changed for some 70 mesh wire screen. This is to get a more consistent heat input, since the wire mesh won't change its shape and it's not burning either:


The engine was then connected to the eddy-current-prony-brake-dynamometer ;D:


The engine working hard:

And the power curve:


Mechanical power output peaked just shy of 0.8W at roughly 1000rpm. I think for a Stirling engine of this size and with this kind of heater, this is not too bad.

Plani

Offline MJM460

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Re: Rocker V Stirling Engine
« Reply #69 on: July 08, 2018, 08:28:02 AM »
Hi Plani, that is pretty impressive performance for a little wick powered engine.  It should be able to power something, perhaps a small paddler, obviously not a steamer.

 Did you try and measure the fuel consumption so you can calculate the efficiency?  I suspect that it will be better than most similar powered steam engines.

The eddy current brake looks great.  Is it a published design?  I can't ever get my head around how they work, but I would like to build one of those.

MJM460

The more I learn, the more I find that I still have to learn!

Offline Zephyrin

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Re: Rocker V Stirling Engine
« Reply #70 on: July 08, 2018, 10:04:58 AM »
Great work with the power measures, very interesting, such data are scarce with ours little engines...

With Audacity, amongst the analysis tools, there is a frequency spectrum analysis, a fast Fourier transform, that gives (with good recordings )a clear peak  of the fundamental frequency, and with the first video, a sharp peak at  29 Hz clearly emerges and other peaks at 58 (x2) 87(x3) etc. hence the 1750 rpm.
and in the video with the brake, the peak at 16 Hz and 960rpm, is obvious as visible on the picture.

but as it analyses the sound only, this could be misleading, ie for a 4st engine, it gives half speed  !

https://sourceforge.net/projects/audacity/

Offline b.lindsey

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Re: Rocker V Stirling Engine
« Reply #71 on: July 08, 2018, 06:17:04 PM »
Beautiful engine Plani and what an impressive runner!!!

Bill

Offline Plani

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Re: Rocker V Stirling Engine
« Reply #72 on: July 08, 2018, 08:46:09 PM »
Thank you, Bill  :cheers:

Zephyrin, thank you very much for the link provided. That's a nice tool to have in the toolbox to do such investigations  :cheers:

MJM460, I was thinking about some freestyle G-Scale loco for this engine. I think power would be sufficient.
Good point about the fuel consumption. I actually didn't bother to measure it during this run. I will do another run and then the burner will get weighted before and after to determine the burn rate and thereof the power of the flame. Any guess about the efficiency  ;)?

The Dyno is my design. The working principle is actually pretty simple. On one side of the pivot arm there is a strong magnet in front of the aluminum disc. When the disc is moving, the magnet induces eddy currents into the disc. These currents produce a magnetic field, which in turn act as a force on the magnet (just try once to slide a strong magnet down some aluminum sheet, or dropping it through an aluminum pipe). This dragging force is then picked up by a load cell which is place at a certain distance from the pivot. So from that we get the torque. The magnet sits at the end of a thread, so the torque can be adjusted by placing the magnet closer to the disc. There is as well an optical sensor to measure the speed of the disc and the the electronics just calculate Speed x Torque = Power.


Inside the Pivot there are 4 ball bearings in order to measure the drag of the disc bearings too:


I think to measure such small powers this is necessary, but the design is not optimal. Because of these four bearings in line, the disc tends to vibrate and this makes the measurement noisy. In a next version I would stick to the principle, but I would choose another set up of the bearings to get more stiffness.

Plani

Offline MJM460

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Re: Rocker V Stirling Engine
« Reply #73 on: July 10, 2018, 12:43:04 PM »
Hi Plani,

I think I can cope with that.  I assume you used a Tecscan force sensor or something similar with operational amps and an Arduino.  Or did you program a micro controller as a stand alone?  I think It could be done with Picaxe, which would be my choice, or Arduino if necessary.

Any requirements for the thickness of the disk?  I will keep thinking about that spindle system, but no really my area. 

By noisy signal, do you mean the torque fluctuation inherent in the engine, or physical noise?  It might be possible to smoothe the force signal fluctuation with a resistor-capacitor arrangement as a filter/averager.

No idea of the efficiency, but I think it could be a lot higher than my little oscillating steam engines, as you don't have to evaporate the water then throw away the latent heat in the exhaust, and it is a very high proportion of the total burner output.  I will be interested to learn how much fuel you burn per minute.

MJM460


The more I learn, the more I find that I still have to learn!

Offline Plani

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Re: Rocker V Stirling Engine
« Reply #74 on: July 10, 2018, 08:41:44 PM »
Hi MJM460

I just used some load cell from China. It was set up with a instrument amplifier to get some reasonable output. This is then read by an analog input of the micro controller. I'm using one of the same family as the arduinos, bur with another programming environment.

The thickness of the disk is not critical. It has to run true and for greater loads it has to be able to absorb the power in form of heat.

By noisy signal, I meant erratic readings of the load cell because the whole apparatus started vibrating. Some averaging is done in software to get a smooth reading.

So, and in the meantime I did another run with the Engine and I recorded the fuel consumption: During a run of 10 minutes the burner used 2.3 grams of burning alcohol. Wikipedia states the heating value of ethanol to be 26.78MJ/kg.
If I've done the calculations right, that means that the little flame has a power of 103W.
Follows the gross efficiency from fuel input to mechanical output of 0.78%

Plani