Caloric Engine Design

[joeby]

Well, this weekend hasn't been very productive as far as shop work. I had plans to get some things done on one of numerous projects; but just didn't get there. Anyway, with the weather and all, and the shop being a little colder than I like, I thought I'd add another project to the pile.

I really took a liking to IronHorse's Caloric engine, and thought I would see what I could come up with. Between reading his comments and what I could dig up on the internet, I figured I would try to make a few "improvements" in it. Obviously his engine does what it's supposed to do and lacks nothing in appearance so what's there to improve upon?

One comment I noticed is the heat buildup. I don't really want to add water cooling to the engine. Cooling fins on the cold end of the displacer would seem to help, without having the engine look too cluttered. Another consideration with heat transfer is having a one piece displacer cylinder. I was going to try making it two-piece with possibly a stainless hot-end and a copper or brass cold-end. I haven't thought much about the displacer yet. I have seen them built up from different materials also (to slow heat transfer); but I wonder if it's worth the work?

I planned on adding "porkchop" weights to the crankshaft; but crankshaft design isn't familiar territory, so "poke and hope" engineering applies here. I think the ones I planned for may be overkill.

Anyway, I've gotten about a days worth of ass time into this project, and although I think I have a reasonable idea of where I'm going, I would appreciate any comments or criticisms on this as I go along. I'm going to try to attach a screenshot of what I have so far.

Have a look, and let fly with any comments.

Kevin

 

[SignalFailure]

Hi Kevin

These designs are pretty much the same as the simplified Henrici engines which weren't mechanically efficient but were quite popular because they'd burn anything I doubt if there's much room for improvement in efficiency other than using modern lightweight and low friction materials/bearings and maybe piston rings.

As these are low pressure engines (usually operating +/- atmospheric pressure) the cylinder might benefit from a slightly larger bore, it looks a little small in your drawing.

I'd definitely try to stop heat creeping to the cold end in whatever way you can come up with.

I suspect that's a problem I'll have with my work in progress (http://www.homemodelenginemachinist.com/index.php?topic=3598.0) although I do have a water jacket that I eventually hope to use the engine to pump water through. We'll see!

Good luck with your project!

PS I'm using a 'barrel' displacer but other have used stainless-type 'pan scourers' between discs or a stack of discs with randomly placed holes as regenerators.

 

[joeby]

Paul,

Thanks for the reply.

The Stirling engines have got my interest, for the time being anyway, because of their simplicity (if you could call it that). I can find the time to work on them and modifications are relatively easy. I have a few built, one is a LTD, the other is a scaled down Moriya fan. I like to think I've learned a little from those two; but things like displacer volume vs power cylinder volume have me stumped still. Is there a "best" ratio?

The displacer cylinder as I have it drawn has cooling fins on it; but they're difficult to make out. The displacer will be 1 1/4" diameter and the power cylinder about 5/8". I figure I'll use steel for the piston, considering graphite instead though.

I haven't seen anything other than a "barrel" type displacer. Would a disc type be as efficient?

Keep us posted on your project! Looks to be coming along nicely!

Kevin

 

[mklotz]

Re: Is there a best ratio?

This has been discussed before. Take a look at reply #12 in the following thread:

http://www.homemodelenginemachinist.com/index.php?topic=2380.0

 

[SignalFailure]

Kevin, my understanding is that you want the regenerator to cause the active volume of air to give up it's heat as quickly as possible so the greater the surface area of the regenerator the better. If you do a search on 'laminar flow' or 'acoustical heat' engines I'm sure you'll find lots of interest. ;D

I'd also recommend this page with regard to ratios...

http://www.geocities.com/kenboak/Manson.html

When I get time I'm going to make one - there's a simplified schematic on my website.

If you went the 'holed disc' regenerator/displacer the trick is to drill one hole through a stack of discs then mount them with washer between each, rotating each by a random amount as you assemble them.

Re=reading my original reply I think it came across a bit negative - with the expertise of others on this forum I'm sure there's room for improvement and enhancement of these engines.

Good luck!

 

[joeby]

Marv,
Thanks! I read the post, and it was just what I was looking for. Now that I know what will work, I can get the rest of the engine drawn up. Maybe a good project for tomorrow with freezing rain in the forecast again.

Paul,
Thanks again. I will do some reading and see what I can come up with. The disc type displacer I might make also, not much of a job to swap displacers.
By the way, I didn't catch the "negative" aspect in your reply. These engines aren't capable of much power output, unless pressurized as I understand it, so having one that runs is well enough. I'm just looking to increase my chances of having this thing run "as built".

Kevin