Engine running for short period

Discussion on Stirling or "hot air" engines (all types)
Post Reply
danne
Posts: 3
Joined: Sun May 13, 2018 9:19 am

Engine running for short period

Post by danne » Sun May 13, 2018 9:32 am

Hi!

We are a group of people who are building an alpha stirling engine as a schoolproject. The heat is generated with a burner and cooling is done with water through channels around the cold cylinder. The problem we have is that engine runs well for about 3 minutes and then stops. If we try to start it again it runs poorly for a couple of seconds and then stops again. From the data we collect we can se that the hot airs temperature is about 300 degrees celcius and on the cold side it rises to about 100 degrees celcius while the engine is running. Could the problem be that the cold sida gets too hot and starts building up a pressure due to this that stops the engine or do you guys have any other ideas?

Blaf
Posts: 30
Joined: Fri Mar 02, 2018 2:50 am

Re: Engine running for short period

Post by Blaf » Mon May 14, 2018 1:39 am

I would guess either insufficient cooling as you mentioned or thermal expansion of pistons increases friction to a critical level.
What materials have you used for pistons and cylinders?

danne
Posts: 3
Joined: Sun May 13, 2018 9:19 am

Re: Engine running for short period

Post by danne » Mon May 14, 2018 2:05 am

Increased friction could be a factor, good point! Cylinders and pistons on both sides are made of steel. The displacer on hot side is made of stainless steel.

Ian S C
Posts: 2137
Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: Engine running for short period

Post by Ian S C » Mon May 14, 2018 4:26 am

One of your problems may be that your power cylinder and piston are like metals, generally this is not good practice, you should make the power piston from cast iron. As metals go the only one that can be run together is cast iron, second best is cast iron and steel.
What do you do with the water in the cold end, do you have a radiator, or cooling tower, or do you just use a flow of water from a tap. The easy bit is getting the heat into a motor, the tricky bit is getting it out again, and that is just as important as getting it in
Ian S C

danne
Posts: 3
Joined: Sun May 13, 2018 9:19 am

Re: Engine running for short period

Post by danne » Tue May 15, 2018 10:23 am

Unfortunately we don't have the time to make new parts now but that will most likely be helpful advice for next years group!

At the moment we have mounted a cylinder with guide vanes around the cool cylinder. The vanes forces the water to run 2 laps around the cool cylinder. We have also milled out cooling channels in the top of the cool cylinder where water is also runing through. We are gonna try and take the hose where water runs out of the cooling channels in the top and pour that water on the transferpipe to cool the air even more. You certanly have a point in what you are saying... We have no problem heating the thing but cooling is a struggle.

Ian S C
Posts: 2137
Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: Engine running for short period

Post by Ian S C » Wed May 16, 2018 2:12 am

The cooling system has been one of the main problems in using Stirling Engines in motor vehicles.
As for the piston, you might be able to modify it to reduce friction. If you can remove the piston and support it in the lathe so that you can put a number of grooves, about .010" in width and depth on the piston's skirt, put them about 1/4" apart. In engineering terms these are known to form a labyrinth seal. At the same time polish a little more of the piston with very fine "wet and Dry" paper, a few tenths of a thou will make a difference.
The only time steel on steel can be used is when a low to medium carbon steel is run against hardened high carbon steel, or a lower grade case hardened.
This is my ALPHA motor, in it's current form, I replaced the water jackets with aluminium, finned sleaves. In it's old form it would run all day with no water in the system.
Ian S C
[img]
DSC01351.JPG
DSC01351.JPG (139.44 KiB) Viewed 386 times
[/img]

Post Reply