Sterling

Sterling engines do not use liquid. They use ordinary air or some other gas.

Is there an optimum hot chamber/cold chamber ratio for this type of engine?

'Don't really know. From what I've seen there doesn't seem to be any. I haven't seen any formulas for calculating dimensions but a good theorist (which I obviously am not) would be able to get these easily.

I suppose it will be the size of the gas hot:size of the gas cold factoring in a retardation of a nats to be more powerful or something along those lines! I've never made one but I would like to! I've been hunting on the net and cant find that magic number anywhere! Lets hope a theorist reads this post eh!

Hi Vulcan. As a rule of thumb the Beale number is hard to beat: P=0.015p x f x Vo Where P= engine power, p= mean cycle pressue (bar), Vo= displacement of power piston. Otherwise, one has to consider the Carnot efficiency which is: n= (Tmax-Tmin)/Tmax. I hope that this helps. Spencer.

"Is there an optimum hot chamber/cold chamber ratio for this type of engine?"

Stirling engines operate between H1 the high temperature heat source and H2 the low temperature heat sink. Work, W or output is the difference between the two. The greater the difference between the source and sink the more work that can be done.

The maximum possible work output is predicted by the Carnot efficiency which applies to any and all heat engines.

Carnot Efficiency

Hi Vulcan. In 1931 a fellow named John Malone designed and constructed a stirling engine where the working was water instead of a gas. They were slow reving, working at from 25 to 250rpm, the working pressure of the fluid was between 6.8MN/m2 (1.5 tones pr sq inch ) to a maximum of 27.4MN/m2 ( 6 tons pr sq inch ). These engines were used to pump water. Spencer.

I believe you're describing a Fluidyne engine (not sure if I got the spelling right). It's similar to a Stirling but can use liquid.

Hi Vulcan. No! I am refering to a piston/displacer engine, I know what a fluidyne is I have built many. They were invented by Colin D. West of Oliver Springs, Tennessee. Spencer.

I could be wrong, but one thing a Stirling or other hot air engine needs is 'compressible fluid'. Typically air or other gas. Most liquids don't seem to compress very well. That is pretty much why hydrolics works like it does.

But then again, my uderstanding could be totally off base.

Two points:-

1) I think you meant to write Stirling, not Sterling motor (The Stirling engine was invented and developed by Reverend Dr Robert Stirling and his brother James, an engineer, over several years starting in 1816.) So its quite an old design!!!

2) The efficiency of the motors is enhanced by the "difference" in temperature between the hot and the cold cylinder (Generally they have two cylinders, but not always!!!)

By the way, if you are really interested in a cheap version to understand better how they work, look at:-

http://www.ohgizmo.com/2007/08/13/paper-engine-runs-on-heat-or-cold/

Its basically a paper cutout version that actually runs on the heat from a cup of coffee for example. Video is on the URL too.....

Referenced from Wikipedia:- http://en.wikipedia.org/wiki/Stirling_engine

Mr Andy,

Good replay !

Stirling not Sterling

Right! Funny how one could miss that. I revisited my Stirling bookmarks before posting my first answer and totally missed the spelling! Thanks.

I have one on my wood stove to circulate air driving a fan, and they have virtually no torque. The super scientists 15 minutes from my home at Sandia National Laboratories are trying to get the torque up with sun concentrators and engine designs both. Their web site is interesting. We might be a way off yet for any type of pump powered by a Stirling engine that you or I could afford.

Hi PetroPower. I beg to differ. Here in the UK many homes have a water boiler that uses gas to heat it, the residual heat is used to power a stirling engine to generaye their electricity. Spencer.

Ooops. I stand corrected ! But you guys in UK are more clever than us Americans !

I guess it depends on what we call 'power' but for me to buy a Stirling to generate 7-10 kW, and the amount of heat I would need, it seems I'm way off on economics. Mostly because I don't have a heat source other than sunlight. I don't have district heating in my city, so I only have the heat from the sun and the sun 'concentrators' are rather expensive as well.

If you know of a 6 - 10 kW (12,5 kVA) here in USA for cheap, 220 volt 60 Hz single phase powered by sun, please advise.

Never heard of that before! Are you talking about the electricity for the house or the electriity for the electronic igniter for the gas heater? If it is for the house, can you get us a photo?

This is one for you:-

http://starspin.com/stirlings/jimd6.html

I have some other links too, but i will first check if someone else has already added them...

"This is one for you: <http://starspin.com/stirlings/jimd6.html> "

The Jim Dandy #6 was sold a few years ago and is somewhere in Wash. D. C.

It was built from scrap and junk parts scroundged by Jim Symansii using a photograph as a guide. Jim was a craftsman par excellence.

yes i agree, I've seen quite a few home made generators and small production units. particulalry on boats where they use the engine exhaust as the heat supply. I suspect engines with catalytic converters would be excellent for this. there is a good book called 'Stirling engines' by GH Reader & Hooper which gives all the design information you will need; including the fluidine process. Both fluid and gas need to be highly viscous and/or very light weight. The fluids need also to have a wide enough fluid temperature range so as not to freeze or boil in the machine.

"'Stirling engines' by GH Reader & Hooper which gives all the design information you will need"

Where, pray tell can anyone obtain a copy of said book? Amazon doesn't list it and that iindicates it is so out of date as to be unobtainable.

There is another book that might help, goto:-

http://www.stirlingengine.com/

There is another book that might help, goto:-

How I Built a 5-HP Stirling Engine

Be sure to download Chapter 6 from the above book free.

Around The World by Stirling Engine

I have both as well as a MM-5 Coffee Cup Stirling and a MM-7 LTD Stirling.

"Wat is the composition of the liquid used in a sterling engine ."

The liquid is a "FLUID" called AIR, composed of 80% N2 and 20% O2.

"I could use it in my sun-heated pump"

Now that depends on the specific design of your sun-heated pump.

Hi Stirling Stan,

In most modern stirling engines the fluid (gas) is Helium, but the best gas to use is Hydrogen, this is because the difference in fluidity between H2 and air is the same as water vs treacle. H2 also has very high heat transfere properties, but the problem with using H2 is that it will leak through almost anything, especially when it is pressureised, think 110kg/cm squared.

When the heater head reaches higher temperatures 600C to 700C the H2 will dissimilate as it passes through the heater wall as H, after it has passed through the wall it instantly assimilates to H2. Hydrogen can also begin to build up in the engine sump, this as you can imagine is highly explosive.

Helium on the other hand has only just less fluidity than H2, and it does not leak from the engine so easily.

Plain atmospheric air is a very sluggish combination of gasses, but it has the great advanage of being virtualy free. But air has not got the high heat tranfere of H2 or Helium.

Spencer.

Non air engines are better thermally. They also have additional 'sealing' problems. Lower molecular weight gasses leak a lot more easily.

I notice in the 'How I built a 5HP Stirling Engine' book they syphon off a little energy to run a pump to pressurize the crankcase (and since it is a gamma type enghine, the cylinder as well). This increases the thermal mass to make it more efficent. Not that H2 or He would not make it better, this seems to be a 'reasonable backwoods' efficency generator. Their goal was to run an engine away from 'technology' in the rice fields of the Far East.

Appropriate technology for their mission.

Hi servant74,

Yes I do understand that, as I have been designing and constructing stirling engines for over 25years. The largest of these is a 20hp engine for the 27ft boat I used to own. I have experimented on alternative fuels ie, wood chippings, logs, other bio-mass and methane comming from landfill sites.

Spencer.