LTD Stirling running on ice

**mklotz** · Oct 17, 2020, 01:14 PM

A recent acquaintance scoffed when I told him I'd built an engine that could run on ice so I made a short video to prove it...

As you can see, I'm not an accomplished videographer (I don't do it for money :-) but at least I used a tripod and the background music is classical at a very low volume.

Some details on the engine...

The displacer chamber where the air is alternately heated and cooled is at such a low pressure that, instead of gaskets, it was sealed with a bit of Vaseline smeared on the end plates prior to assembly.

The engine can't be lubricated. Even turbine oil is viscous enough to overpower this extremely low power engine. The power piston is made of self-lubricating graphite; this is a common practice in these LTD engines. The main shaft linking the power piston and displacer drive runs into miniature ball bearings of the type used in gyros in high-end inertial reference platforms.

Below is a picture of the drive side of the engine...

LTD Stirling running on ice-ltd-stirling.jpg

**Tonyg** · Oct 20, 2020, 08:21 AM

Nice work, what are the tolerances on the power piston.

**mklotz** · Oct 20, 2020, 09:01 AM

Originally Posted by Tonyg

Nice work, what are the tolerances on the power piston.

The short answer to your question is "I don't know".

I first bored and polished the cylinder. Then I rough turned the graphite piston to close to the bore size. Final sizing of the piston was done by "sanding" it with a piece of brown paper cut from a grocery bag until it fit well in the cylinder. After removing the piston from the parent stock I tested it by weighting it with a BB and letting gravity pull it down inside the cylinder. It descended very slowly so I called it good and never measured it; I didn't want to risk applying a metal micrometer to a tiny, delicate graphite piston.

**Tonyg** · Oct 20, 2020, 09:20 AM

Thank you Marv, it must have been a real fun project. I have been a great admirer of your input on this forum.

Kind regards,

Tony.

**jdurand** · Oct 20, 2020, 02:02 PM

The commercially made stirling I have here uses a ground glass piston in a glass tube. I have no idea how close that's matched but it works really well. Been using it to time my tea steeping for years.

**nova_robotics** · Oct 20, 2020, 07:07 PM

I bought one of the eBay/Amazon small Stirling engines and tried to lubricate it a few different ways. Mirroring exactly what you said, most lubricants are too thick and create too much drag. A very light pneumatic tool oil seems to work though.