Stirling Engine : Laura

[Brian JohnParticipant @brianjohn93961]

Today I made a paper gasket for the work cylinder cover. I need much more practise in making gaskets ; it is harder than it looks. But first I removed the work piston and cylinder to test it : I placed one end on my thigh to seal it up and pushed the piston down from the other end. It gives a very good seal with lots of ''spring'' as the piston is compressed so there should be no problem there. I do not need to make another work cylinder and piston. After fitting the gasket I noticed that the cylinder cover was not quite sitting correctly so I removed the gasket and it was still not sitting correctly. I then put the cylinder cover in the lathe and machined it to a smooth finish then tried it on the engine without the gasket. Huge improvement….but it will still not run !

I was previously getting air leakage around the work cylinder cover ; the engine now makes a different noise…sort of ''put put put''. I am now getting 8 revolutions when the engine is cold and about 24 revolutions with heat applied. When I try turning the flywheel in the other direction it will only turn twice so I have fixed a major air leak but there may be others.

I am still not happy with using Hylomar as there is no way of knowing if all has been sealed adequately between the cylinder holders so I am going to have another go at making a paper gasket for this. I have also purchased some Permatex high temperature silicone gasket compound but I will not be using this just yet. I think a paper gasket would be better if I can get the shape correct.

Edited By Brian John on 23/02/2016 06:50:33

Edited By Brian John on 23/02/2016 06:52:20

Edited By Brian John on 23/02/2016 07:07:42

[Neil WyattModerator @neilwyatt]

Bear in mind that Roibert Stirling had to pressurise his engines to 360 psi AND he had complex regenerators fitted to the displacer pistons before he could get them to rival/beat steam engines.

He was a very clever man.

Neil

[AjohnwParticipant @ajohnw51620]

On the other hand Neil millions have been spent on them even for eventual use on prime movers but they don't seem to be in use. NASA I understand uses them to generate electricity – the free piston types that are shown on youtube made out of tin cans.

Hylomar doesn't really set Brian so if you can get a thin narrow strip where needed it will flatten and spread when the screws / bolts are tightened. Red Hermatite may be easier to use. That would be a bit more difficult to remove if you need to.

John

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[Ian S CParticipant @iansc]

Brian, the tube of gasket goo in your link, or the Loctite liquid gasket in a tube would seal the two bits that form the cylinder heads. Have you got something that you can drive the motor for say half an hour (not your Dremel), at a few hundred rpm?

Ian S C

[Brian JohnParticipant @brianjohn93961]

Ian, I am sure that friction is not my problem now. When the flywheel is flicked by hand then the engine will spin for about 8 revolutions unheated with both piston rods fully connected ; the instructions say 5 revolutions is about right. I think I still have some air escaping from somewhere….just enough to stop it from working.

 

Edited By Brian John on 23/02/2016 13:25:21

[Neil WyattModerator @neilwyatt]

Posted by Ajohnw on 23/02/2016 11:31:17:

On the other hand Neil millions have been spent on them even for eventual use on prime movers but they don't seem to be in use. NASA I understand uses them to generate electricity – the free piston types that are shown on youtube made out of tin cans.

The main problem is that although they are more efficient than internal combustion engines, they are also generally much heavier and less suitable for applications like cars where rapid changes in speed and torque are needed.

I just found this: en.wikipedia.org/wiki/Applications_of_the_Stirling_engine which has some interesting examples, and this is an eye-opener: ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19880002196.pdf

[AjohnwParticipant @ajohnw51620]

There are some thesis's about Neil – including design. The simulations seem to work but not sure about the engines. I wonder if the fuel economy included petrol lean burn. It was getting there but the gov said no cats instead. Mustn't steal Brian's thread

John

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[Brian JohnParticipant @brianjohn93961]

Very frustrating : it wants to run but there is still a problem there. I assume that there is still air leaking from somewhere as I think there should be more resistance when I turn the flywheel by hand. I have ordered some 3mm silver steel rod from Minitech as per Hopper's suggestion. This will be used for the D. piston rod. The current piston rod is probably a bit undersized as discussed above so the 3mm rod should give a better seal.

While I am waiting for that to arrive I will start making up paper gaskets for the cylinder covers in case they are needed as well.

NOTE : I did think about leaving this engine alone and moving onto another project but I just can't…I have to get this to work. I feel that I am very close.

[JasonBModerator @jasonb]

Brian have you tried mixing a little washing up liquid in some water and brushing it around all the joints. Then turn the engine over and any leaks will make the liquid bubble.

Try translating this page

[Brian JohnParticipant @brianjohn93961]

I have tried the soapy liquid and I cannot detect any leaks anywhere but I have just noticed that when I spin the flywheel that the burner flame moves away from the engine. I should have seen this before. There must be air leaking from around the rubber O ring that holds the glass tube in place. This is the last place I expected there to be an air leak ; the glass tube is a very tight fit against the O ring. It could be that there is air leaking from between the O ring and the brass collar that holds it in position.

While am thinking about that I have made some further adjustments by moving the work piston back from the cylinder head (two full rotations of the piston rod) using the thread and lock nuts I put on the piston rod….. huge improvement ! I am now getting about 8 seconds of running. I cannot estimate the number of revolutions. At one point I really thought it was running on its own but then it slowed down.

I am not sure what to do about the O ring but I will have a close look at the brass collar tomorrow.

Is it worth advancing or retarding the timing on a Stirling engine or is that a waste of time ?

Edited By Brian John on 24/02/2016 12:35:20

Edited By Brian John on 24/02/2016 12:37:28

[Ian S CParticipant @iansc]

Maybe a bit of RTV around the area of the o-ring might do the trick.

With some of my early motors I ended up with a sore wrist flicking them over, then fiddle around a bit, try again, give up for a day or two, light up, give it a flick, and off we go bl$%dy marvellous. Others, light the burner, give it a flick, and it goes, almost boring.

Ian S C

[Brian JohnParticipant @brianjohn93961]

RTV ?

[JasonBModerator @jasonb]

RTV your silicon sealer will do the same as Room Temperature Vulcanising (setting) rubber

Although the ring may be tight around the tube it also needs to either be tight where it fit the hole on its OD or the recess needs to be slightly shallower than the O rings cross section so it is squashed tight as the screws are done up

[Brian JohnParticipant @brianjohn93961]

Yes, I will pull the collar off tomorrow and have a look. I may have to machine a bit off the inside surface to make the recess shallower.

I keep thinking about that youtube video where the guy had 8 socket cap screws on the collar and not four as per the instructions : perhaps he was onto something ?

Edited By Brian John on 24/02/2016 13:47:20

[Neil WyattModerator @neilwyatt]

I still think that the sloppy displacer rod needs sorting before anything else. Have you tried seeing if it bubbles around it with jason's soapy water suggestion?.

[Brian JohnParticipant @brianjohn93961]

Yes, I did not see any bubbles forming there but I have still ordered some 3mm silver steel rod from Minitech anyway.

[Brian JohnParticipant @brianjohn93961]

I have re-machined that brass collar holding the glass tube. It was not deep enough at 1.1mm ; now it is the required 1.4mm. The flame is holding steady so I assume that I have fixed the air leak there. It still will not run but I have now got it up to 12 seconds so there is some improvement. I will have to wait for the 3mm silver steel rods from Minitech to arrive for further experimentation.

I also bought some JB WELD high temp RTV. I did not know they made this product. I will use this if I still cannot get the engine to run after replacing D. piston rod.

[AjohnwParticipant @ajohnw51620]

I was nosing at J Ridders's site yesterday and noticed a comment about one of his designs that is loosely similar to yours. He mentions that the use of glass tubes allows the use of o rings as the glass prevents them from getting to hot.

Doesn't sound like you are having an o rings got too hot problem Brian but it might be worth people thinking about that before getting the propane torch out.

If you moved the power piston back along the con rod you also changed the compression ratio – reduced it which loosely means that less temperature is needed to get it to run. The run on the hand types use extremely low compression ratio's. J Ridders mentions this in a different way. It also mean less power though so changes in either direction might help. This area is why concentric same cylinder ones are reckoned to be more efficient / powerful, they have less dead space allowing higher compression ratio's. It seems this can be as high as 1.1 to 1.2 on any engine. LT ones more like 1.xx with some 0's before a number rather than x's.

John

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[Brian JohnParticipant @brianjohn93961]

I have no intention of using a propane torch. It gets hot enough with the meths burner. Increasing the heat input is not the way to go.

I might move the power cylinder back a bit further tomorrow ; it is worth taking a few minutes to experiment.

What do you mean by ''concentric same cylinder ones'' ?

[AjohnwParticipant @ajohnw51620]

Like this

https://www.youtube.com/watch?v=MrArmbBIe5Q

 

John

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Edited By Ajohnw on 25/02/2016 15:21:06 – can't get the video to show even after 2 goes

Edited By Ajohnw on 25/02/2016 15:24:02

Edited By Ajohnw on 25/02/2016 15:25:06

[KettrinboyParticipant @kettrinboy]

Hi Brian

John means Beta type engines where the power and displacer piston run in the same cylinder with the displacer rod running in a bush through the power piston so they are sometimes called concentric engines i have built one and the compression is so high its hard to turn over yet with a flick of the flywheel it starts easily and runs fast ,  your engine is a Gamma configuration where the two cylinders are separate and connected by a pipe or passage , anyway i think when you get the displacer rod and bush fit sorted theres a good chance your engine will run.

regards Geoff

Edited By Kettrinboy on 25/02/2016 17:39:59

[Brian JohnParticipant @brianjohn93961]

After sorting out the problem with that airleak around the O ring I decided to restore the power piston to its original position ie. two turns closer to TDC. After I had done this, I put the flame on and began oiling all moving parts. I was only moving the flywheel very slowly and it started to run………..Success ……sort of !

On the first run, the glass tube blew off after about 60 seconds. This is a video of the second run ; the engine will only run for about 4 minutes before it stops. I suspect that, being another very hot day, too much heat is being transferred to the power cylinder.

Possible solutions are ;

1. Make a cork gasket so that the glass tube can seat up gainst this rather than being pressed firmly onto the end of the D. cylinder. This might interfere with the good seal I now have on the O ring.

2. Make a cork or paper gasket to fit between the base of the D. Cylinder and the cylinder holders (frames). I am leaning towards this idea at the moment.

Anyway, we are nearly there. I was quite shocked when it started to run by itself …I was not expecting it at all. Tomorrow I may give it a go with a tealight candle before trying to make those gaskets.

**LINK**

 

Edited By Brian John on 26/02/2016 05:53:49

[Michael GilliganParticipant @michaelgilligan61133]

Congratulations, Brian

MichaelG.

[JasonBModerator @jasonb]

Well done Brian you got there in the end. You could just move your burner nearer to the end of teh glass tube, this will put less heat into the engine and should also see it running a bit slower.

J

[pgk pgkParticipant @pgkpgk17461]

Well done. I said you'ld get yours working first

I wonder if part of the problem is the same as i hit with my temporary brass tube power cylinder… expansion from heat losing compression. The problem then being whether that is from heat through the brass or just the new internal temp when the air temps equalise. Cooling the power cylinder might show longer performance.

What is your power piston made from and does it have the same expansion coefficient?

I've also experienced the displacer cylinder glass coming adrift once the heat moves through..again i wonder if that's partly due to expansion of it's holder.. so less might be more (when it comes to heat) and the differential improved by colling the cold end.

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