# Thermal Lag Engine POC



## mklotz (May 27, 2008)

I've wanted for a long time to build a Thermal Lag Engine (TLE). I have a physicist's fascination with heat engines and the TLE is even simpler in conformation than the conventional or Ringbom Stirlings. I just "hadda have one". 

I got a copy of Jan Ridder's plans and some other information from the web including the original patent for this type of engine. It quickly became apparent that, just as with most everything, the size of test tubes is not standardized. The ones in my collection (left over from building a perfusion machine in high school - a story for another time) aren't anything like Jan's. Moreover, all of these plans admit that a certain amount of fiddling with the design will be necessary. The engine isn't well enough understood to allow for theortetical models of all the "fiddling" parameters so designing in the conventional sense isn't possible.

So, just like any good systems engineer would do, I decided to build a Proof-of-Concept (POC) engine to see if I could get anything to run and, if so, be able to easily fiddle with all the parameters to get a handle on what mattered. Once the POC works, I should know more about what I'm doing and can then go on to build a proper engine.

The video shows the engine. It's nothing more than a test tube with an aluminum cylinder attached via a spigot. The spigot is fitted with two O-rings that seal the test tube to the cylinder. A (critical) aperture in the spigot allows the cylinder to communicate with the test tube. Inside the cylinder is a (critical) lump of stainless steel pot scrubber that acts as a regenerator, although I'll freely admit to not completely understanding what a regenerator accomplishes in that location - I think it's more of a heat retention device.

Inside the cylinder is a graphite piston which connects to a flywheel via a conventional crank. The bits and pieces are temporarily cobbled together on a fixture plate and various setscrews allow nearly every dimension to be adjusted. I had intended to fit the aperture with a means of inserting various size orifices but I lucked out and my first guess produced a working POC. I may yet go back and do that to see if I can further optimize the performance.

And that's it... no valves, no displacer. Just a piston in a closed cylinder. The test tube is heated at the end of the regenerator via an external heat source (alcohol lamp in my case) and the damn thing runs! I don't have time right now to discuss why it works but it's basically the Otto cycle - the working fluid (air) is compressed at a lower temperature, heated, and then expands at a higher temperature. If you plot that on a P-V diagram you'll see that the closed cycle has a net area and that area corresponds to the work done on the flywheel.

If you decide to build a TLE, I strongly suggest that you build a POC first. These engines have very low specific power and thus are sensitive to friction as well as their innate sensitivity to the overall geometry of the engine.

[ame]http://www.youtube.com/watch?v=3DF9gNCavKs[/ame]


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## zeusrekning (May 27, 2008)

If that is just your POC I can't wait to see the final build. I highly suggest red and blue rhinestones to symbolize the hot and cool cycle.
Approximately what size is this motor?
Looks great,
Tim


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## Bogstandard (May 28, 2008)

Marv,

That is truly wonderful. So basically only three moving parts.

I honestly believe that when everything is done and dusted with fossil fuels, these sorts of little engines will be our saviour.


John


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## Powder keg (May 28, 2008)

Those are so fascinating to watch run) Great job Marv!


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## rickharris (May 28, 2008)

Here is a similar engine but I note that the regenerator is at the piston end???

I am unable to comment on effectiveness as I haven't made one - My assumption was that the pot cleaner just increased the surface area and so the heat transfer to the air.


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## kustomkb (May 28, 2008)

First try? thats great! I haven't got mine running but have moved and am in the process of rebuilding my shop(major pack-rat) Did you use bearings? did you de-grease them? I followed Jan's plans precisely and I think I have a perfect fit on the graphite piston. We'll see when I get back to work (play).

Thanks for the motivation,

Kevin


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## mklotz (May 28, 2008)

Thanks for the kind words, guys. At least here I have an appreciative audience. When I showed it to my wife, I got the usual, "That's nice, dear.". Most women seem to have no appreciation of mechanical elegance.

Tim,

The test tube is 150 mm (~6") so the overall length of the engine is perhaps 12".

John,

Exactly! That's why it's so intriguing. The barest minimum of parts and it's still capable of turning heat into motion. Absolutely fascinating - both mechanically and intellectually.

Rick,

Your picture (with the "misplaced" regenerator) seems to support my contention that it's really more of a heat retention device than a proper regenerator. I intend to experiment with other placements and also try removing it entirely.

For the engine to work, the air has to be heated rather quickly when the piston is hovering near TDC so increased surface area makes a lot of sense.

Kevin,

The crankshaft does indeed run in de-greased ball bearings lubricated with a bit of turbine oil. I had some trouble with pivot friction where the crankshaft attaches to the crank disk.
In the final model, I think I'll put a small ball bearing there too.

The engine has a one inch throw and that seems to work better than my original 3/4" throw. The aluminum flywheel is 3.25" diameter and 0.4" thick at the periphery. I thought that rather large but I believe it could benefit from a flywheel with an even larger moment of inertia. If I can find suitable stock, I may try something larger.

I discovered that the aluminum cylinder has to be warm before the engine will run. I preheat it with the alcohol lamp. I think that, as with flame-suckers, the cold cylinder will "quench" the hot gas too quickly and reduce the available output energy.


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## Brass_Machine (May 29, 2008)

Nice job Marv!

I gotta finish my build on one of those. Thanks for the inspiration. :bow: But where are the rhinestones? Maybe in the final model?? ;D

Eric


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## chuck foster (May 29, 2008)

i just have to stop looking at this web site.............between Marv,john,rick,chuck fellows and almost the whole lot of you guys
i think i have about 200 years worth of projects that i just HAVE TO BUILD :big:

well Marv as others have said if this is you poc than i just can't wait for the real thing ;D  : 8)

chuck


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