I'm sure these are old news to the engineers and mechanical enthusiasts among you, but being that I just fell in love all over again with them and a search turned up 0 results (admittedly surprising), I'm going to introduce many of you to the wide and wonderful world of external combustion.

Warning: If you're anything like me, click away now or you'll spend at least the next hour clicking through videos and links detailing the myriad of implementations.

Synopsis: A simple, dual-piston device that uses a temperature difference to convert thermal energy into mechanical energy. Basically, you make one side hotter than the other by any means and the working fluid, most often plain-ol' air, drives two pistons via a simple 4-cycle thermal expansion-compression process, like so:




-Just to get you hooked, a classic LTD (low temperature-difference) engine running solely off the heat of a person's hand: http://www.youtube.com/watch?v=6DBktwPf3rk&feature=related

-Home-made fun:
http://www.youtube.com/watch?v=KcKeqsKHcdg
http://www.youtube.com/watch?v=q-hqW5umLzo

-Elegant, machined models:
http://www.youtube.com/watch?v=8jbiTZNfGFM
http://www.youtube.com/watch?v=KvHz20lhiBE

-Solar-powered (for you hippies):
http://www.youtube.com/watch?v=nq6iCO9KLKA

-Whimsical experimentation:
http://www.youtube.com/watch?v=VG_RE-o9qzQ
http://www.youtube.com/watch?v=pPrRRm08UrM
http://www.youtube.com/watch?v=cnx_1qFA7OE
http://www.youtube.com/watch?v=AfYpNOEif8I
http://www.youtube.com/watch?v=7SCt3D9fzX4
http://www.youtube.com/watch?v=r7Lin3zXksY

-Big'uns:
http://www.youtube.com/watch?v=mjFbi_dJT6U

-Practical Applications:
-fans/lights: http://www.youtube.com/watch?v=7U5qwT8WrWc
-boats: http://www.youtube.com/watch?v=1YrnzwHBTZ8
-buggies: http://www.youtube.com/watch?v=qS5x91CZbtY
-planes: http://www.youtube.com/watch?v=SX5XOpe8Eas
-pumps: http://www.youtube.com/watch?v=4D7_TRG2Itk

-For mechanical dorks:
http://www.youtube.com/watch?v=TBEkdKBL1TA
http://www.youtube.com/watch?v=F9oQeq54NP8

-zOMG FREE ENERGYS!!!1
http://www.youtube.com/watch?v=8LOeFXZAvNQ


And the list goes on. and on. If anyone wants to buy me a present, I'll take anything off this page:
http://www.ministeam.com/acatalog/Bohm_Stirling_Engines_and_Kits.html


That'll do for now, happy browsing.

[Edited on October 29, 2010 at 3:50 AM. Reason : knew it]

10/29/2010 3:36:53 AM

Tech Talk?

j/k... Chit Chat > *

10/29/2010 3:42:40 AM

Thought about Tech Talk, but I figured I'd reach more unaware and interested people here.

And the Garage is all Subarus and CBRs

[Edited on October 29, 2010 at 3:49 AM. Reason : asdf]

10/29/2010 3:47:55 AM

now I want one

10/29/2010 4:36:13 AM

i wanna make one

not talking about the coffee-can rickety ones, but an honest one machined from brass, aluminum, and/or steel. might whip up something on autocad and see if I can't find someone to help me out in an ncsu machine shop. anyone here have access and the knowhow? is there cnc stuff I could use or would i be limited to lathes, saws and drills?

10/29/2010 4:50:32 AM

so what's their big disadvantage that keeps them from being used extensively?

10/29/2010 6:55:32 AM

http://www.bekkoame.ne.jp/~khirata/english/others.htm

and you can buy a kit for ~$120 (if anyone cares): http://cgi.ebay.com/170558644658

[Edited on October 29, 2010 at 7:58 AM. Reason : .]

10/29/2010 7:57:01 AM

^^b/c they suck compared to auto and diesel engines is the short answer.

We actually didnt even go over these cycles in thermo, but I wish we had. I just checked out the section that deals with stirling and ericsson cycles and there isnt too much info. From what I can determine, they, at the moment cannot be as compact as auto and diesel engines and produce comparative net work output. I'm by no means an expert, but am interested in the subject matter at hand. Add to my topics.

zxappeal should be in here shortly to drop some knowledge i'm sure.

10/29/2010 11:23:45 AM

Carnot stole this idea from Stirling. Maybe.
I'd rather have a Stirling engine.

10/29/2010 12:02:29 PM

I wanted to build one a few years ago. I like it.

10/29/2010 12:59:31 PM

LOL @ TheBullDoza...

You're very right about the whole compact with comparable net work output. The beauty of Otto and Diesel cycles is that the whole compression/expansion cycle takes place in ONE chamber, the one in which combustion occurs and acts directly on the piston. For this reason, otto and diesel engines can be very compact and require very little complex linkages and heat transfer surfaces. The downside is that they are very limited in what they can use for fuel. A Stirling engine can operate off of ANY heat source. The catch is switching heat source and sink rapidly and efficiently enough to provide a steady mechanical work output. It's very difficult to isolate source and sink and not lose efficiency due to heat transfer directly between the two or to the actual machine itself.

Now what might be an interesting concept (at least for stationary use) would be heat recovery using a Stirling cycle in a compound engine arrangement. Think half of the engine burning fuel in a conventional Otto or Diesel cycle (or even Brayton cycle), and the other half using exhaust heat as a Stirling heat source.

I think stationary use is where Stirling would be of the most benefit, simply because heat rejection can be accomplished much easier and at a much higher rate with either geothermal heat exchangers or a large source of water for conventional heat exchange. The higher the temperature differential, the more efficient the cycle. Hmmm...this gets me to thinking quite a bit.

I could puzzle over all this for quite a bit. I wish I had access to all the tooling to experiment and build some of this shit.

10/29/2010 1:19:54 PM

Quote :

"Carnot stole this idea from Stirling. Maybe. I'd rather have a Stirling engine."

Like you have a choice.

10/29/2010 2:50:35 PM

Yeah, what interests me about them (for practical use, anyway) is not for primary-drive applications, they just simply don't put out anywhere near enough power. But in so many mechanical processes we use in day-to-day life, waste heat is generated that is simply dissipated into the atmosphere. The scalability of Stirling engines provides an attractive means of power for low-load auxiliary applications.

Or, pretty much exactly what zxappealsaid

Quote :

"Now what might be an interesting concept (at least for stationary use) would be heat recovery using a Stirling cycle in a compound engine arrangement. Think half of the engine burning fuel in a conventional Otto or Diesel cycle (or even Brayton cycle), and the other half using exhaust heat as a Stirling heat source."

10/29/2010 3:44:27 PM

i wonder how heat recovery with this would compare to the rankine cycle heat recovery currently used on the back end of combustion turbines

hmmmm

10/29/2010 3:49:02 PM

saw the animation, got drowsy, scrolled down, saw

Quote :

"-Big'uns: "

stopped

investigated

disappointed

10/29/2010 3:49:17 PM

well there are big ones as far as size, in that example, and there are big ones as far as power production. I think I remember seeing a 5hp stirling motor on youtube somewhere.

http://www.youtube.com/watch?v=XpqhX_66n18

Running on burning sawdust. Some super-green carpenter could lug one of these around to both clean up after himself and power his lights or air compressor

[Edited on October 29, 2010 at 4:10 PM. Reason : yep]

10/29/2010 3:57:27 PM

( . Y . )

10/29/2010 4:01:38 PM

Quote :

"auto and diesel engines "

pretty sure you mean the "Otto" cycle

10/29/2010 4:09:48 PM

Quote :

"i wonder how heat recovery with this would compare to the rankine cycle heat recovery currently used on the back end of combustion turbines hmmmm"

Lotsa heat recovery going on in cogeneration. Pretty much the same concept, obviously. How would it compare? Would heat recovery on a gas turbine be used for feedwater preheat, or is it used as a superheat stage? I don't know much about it all. My guess is that exhaust temps on a gas turbine would be high enough for superheat.

10/29/2010 4:10:23 PM

We've installed a few stirlings as biogas generators at wastewater treatment facilities and landfills.

It's cool work.

10/29/2010 4:14:25 PM

[Edited on October 29, 2010 at 6:04 PM. Reason : dbl]

10/29/2010 6:04:04 PM

Quote :

"Lotsa heat recovery going on in cogeneration. Pretty much the same concept, obviously. How would it compare? Would heat recovery on a gas turbine be used for feedwater preheat, or is it used as a superheat stage? I don't know much about it all. My guess is that exhaust temps on a gas turbine would be high enough for superheat."

most HRSGs being installed on the back end of CTs have 3 pressure levels (3 steam drums). they have the whole works. economizers, superheat sections, reheaters. 2- 3- and 4-on-1 designs are most common (2, 3, or 4 CTs each with it's own 3-drum HRSG. the steam from the multiple HRSGs comes together in headers and feeds steam to 1 tandem compound steam turbine). the tubing in the HRSGs is finned (convective) instead of radiant like you'd find in a coal-fired plant.

[Edited on October 29, 2010 at 6:04 PM. Reason : adf]

[Edited on October 29, 2010 at 6:06 PM. Reason : adsf]

10/29/2010 6:04:25 PM

they have these at the State Fair (or they did one year).

10/29/2010 7:11:55 PM

i really like the stuff this guy comes up with

http://www.youtube.com/watch?v=borjljcuIuI

10/30/2010 5:13:45 AM