Stirling Engine : Laura

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

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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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

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

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

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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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.

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

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

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

RTV ?

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

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

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?.

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

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.

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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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'' ?

Like this

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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

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