Lamina Engine

[Stan]

I am working on an experimental project and I have now reached the stage where I can do some research on lamina engines.

The tube is 6" long .625" OD and made out of mystery metal. It was in my scrap brass box as I thought it was plated brass plumbing pipe but appears to be a magnetic stainless. I silvered soldered a plug in the end and threaded the other end 32 TPI. I stuffed a bunch of steel wool into the bottom of the tube.

The support post is 7075 Aluminum. A scrap piece just cleaned up, bored .625" 32 TPI threaded all the way through. With the tube screwed in, there is an O ring to make the seal to the cylinder.

The cylinder is 1.125" 6061 aluminum 2" long bored out for a .750" piston and one end stepped down to .625" and threaded 32 TPI. The inside of the step is bored and threaded 3/8" x 16 TPI. I made a plug 3/8" x 16 with a 1/4" hole and an insert with a 3/16" hole. This gave me three choices of restrictor size to try and get the engine running.

The crank assembly is straight forward. Ball bearings with the grease washed out and a 2 1/4" OD aluminum flywheel with six 1/4" brass inserts in the rim to add weight. The flywheel rim is 1/2" wide and the inserts go all the way through. There are two short copper inserts to balance the weight of the crank arm which has a basic connecting rod onto a graphite piston.

I probably spent four hours before I had it running and was intrigued by the fact that when spinning the flywheel, it would always stop with the piston in the middle of its stroke, never at either end. I had expected that heating the tube would cause the air to expand and push the piston out and just sit there, if running conditions were not being met.

The trial run shown in the picture was about 5 minutes with the 1/4" restrictor. Now the fun starts to experiment with different restrictor size, different tube length, different amount of steel wool, etc. On the trial run, I did find that changing the position of the flame along the tube had little effect on speed. Obviously, it will be a long time before final pieces are made and a displayable model assembled.

 

[carbide_burner]

Keep us posted! I must confess that I'm a little envious of you... I'm also busy with a Laminar flow engine as you might have picked up from other threads, but still need a few things before it will run. I'm going to use a glass test tube, that was incidentally delivered today, and have picked up the following info as a (apparently) good starting point:
Test tube-150x25mm
Bore/Stroke-25x25mm
Choke-6mm

Enjoy your engine!

 

[Stan]

Glass test tubes seem to be the norm so my project was strictly experimental. I don't know if the rate of heat flow in Pyrex is part of the secret and since my tube is mystery metal I can't form any conclusions.

BTW: In all the threads and web sites that I have read, I don't remember ever seeing a test tube as large as 150 x 25 mm. There appears to be a relationship between the test tube size and the cylinder size. You will need to do some math to try and come up with a cylinder diameter and piston stroke.

Thia afternoon I measured the ID of my tube (.550") and made a tube 4" long with .5" ID out of 6061 aluminum and it didn't work at all. In fact no indication that it even wanted to work.

 

[Stan]

I have spent the last three weeks experimenting with my lamina engine. I have read hundreds of posts on the internet and there seems to be no definitive theory on how they work so all experiments are empirical.

I have worked with three different heat tubes and three different cylinders with three different stroke lengths. I think I have tried all the different permutations using various sizes and lengths of restrictor.

I am now pleased to report that I not any smarter than when I started. I have noticed several interesting things, some previously reported on other boards. One interesting one is when the flywheel oscillates a half turn back and forth without ever making a complete revolution. This led me to believe that the flywheel might not be heavy enough so a search started for material to make a new flywheel.

Under the garage bench, I spotted an old lathe headstock housing and decided there must be a flywheel hiding in that cast iron. Thinking it only needed some encouragement to expose itself, I used the BFH and got two castings each hiding a flywheel.

Fifteen minutes on the bandsaw got rid of the material that didn't look like a flywheel

After an hour on the lathe I now have two flywheel rims from one bearing seat that will clean up to 4" OD with a 1/2" face. Current plan is to make a brass hub with brass spokes and then I can get back to experiments on the lamina.

 

[Twinsquirrel]

Hi Stan,

Please keep posting your progress, I've been experimenting with laminas as well and like you, I'm still none the wiser. I have noticed a few strange things though..

1. If you get the piston mass just right you can just give it a flick and it will oscillate at very high speed without any flywheel attached, I've been measuring the amplitude of this oscillation in the hope that it will give me the best throw for the crank.... Unfortunately that hasn't worked, yet. BTW I'm building a strobe to allow me to measure it more accurately

2. The length/diameter of the restrictor can change the running properties more than any other variable, you can use this to you advantage to move the hotest point away from the cool parts.

3. My son gets upset when I steal all of the test tubes from his chemistry set.

David

 

[Stan]

David: I didn't disconnect the flywheel when the piston was oscillating but I expect we are see the same thing. Good hint on a strobe. I have a General Radio Strobtach that will stop motion and accurately measure speed. I just have to dig it out and try it.

 

[Twinsquirrel]

Thanks for the heads up on the strobe Stan.

Here is a video of a flywheel-less lamina engine, quite interesting.

http://www.youtube.com/v/cAyw_dOioMU&hl=en&fs=1&rel=0

 

[Stan]

David: Your video is very interesting and a strobe would definitely provide a lot of information. I am assuming, on mine, that the oscillation occurred at the top end of the cylinder (not glass like yours).

If you haven't seen this web site, you might find it interesting. According to the patent drawing, no restrictor was used. The link to models show several engines where it appears that the only restrictor is the necked down portion to fit the test tube.

http://www.stirlingengines.org.uk/thermo/lamina.html

One site I looked at said that too much heat would cause the engine to stop. I admit that in the interest of time, I have used a propane torch to quickly heat up the metal tube. With combinations that were reluctant to run, I have had the tube at red heat and even at orange heat and always found that greater heat resulted in greater speed.

I never ran any long term test as the metal tube and the cylinder are threaded into opposite sides of an aluminum block. I read on one sight that cooling fins were required on the cylinder for long term running.

Lots of delay on model work right now as we approach our winter season and lots of outside work around the house to do before the snow comes. I spent yesterday on a ladder washing the outside of windows. Leaves have to picked up every couple of days and all the garden areas prepared for winter.

 

[Twinsquirrel]

Hi Stan, The video is not mine, it is from a chap called "mowerofdoom" on youtube.

I've seen the design in the link you posted but haven't had a go at making one yet but the other points you make are valid and I have seen from my own tests that if you allow the cylinder to heat up the engine will stop.

David