Puppeteer

Author Topic: Stirling engine revolution  (Read 918 times)

StrawHat

  • Newbie
  • *
  • Posts: 27
    • View Profile
Stirling engine revolution
« on: March 17, 2020, 12:54:54 AM »
For all you folks that have machining capabilities, do you know how ridiculously easy it is to build a free piston stirling engine in the multi kilowatt capacity range? If the main reason you are interested in slow speed diesels is efficient and multi-fuel capable power generation, then the stirlings are definitely a better choice. Frankly, I'm tired of the ridiculous prices people are wanting for dilapidated slow speed diesels that need extensive repairs with only one or two sources of parts here in the US. No chance of any long life expectancies with pre-worn engines due to the limited nature of the repairs possible and those low quality parts currently available either.

Europe seems to be having a stirling revolution. Germany in particular. They have found that by using a stirling to directly drive a regular mechanical heat pump compressor using ordinary freon, and prudent use of counterflow heat exchangers, that a worse case COP of 1.9+ can be achieved! In carefully designed systems they are getting COP's over 2.5! That means for every 1000 btu's of fuel burned driving the stirling, you actually get 2,500 btu's of heat for the house! While it sounds like cheating the laws of physics, remember we are talking about HEAT PUMPS, which harvest heat from the outside in addition to using the heat input.

The EPA can't possibly gripe either without legally entrapping themselves because stirlings satisfy all sustainable energy carbon neutral desires. They can be powered by wood, garbage, landfill methane, any waste oils or fuels and anything that can be burned or that generates heat. Even solar concentrators are used. And to add to the benefit is the fact that most any fuel can be burned cleaner in a dedicated burner than in internal combustion, and considering most fuels rural folks are likely to burn, like wood are carbon neutral.

The theoretical efficiency is over 65% depending on design. You'll working miracles to get 35-40% from any slow speed diesel engine, especially with only 16 - 1 compression ratio's. And that would be only using good quality diesel fuel, not from any alternative fuel.

For me, I'm scrapping thoughts of buying any slow speed diesel. I'll just wait until I build a stirling.

StrawHat

  • Newbie
  • *
  • Posts: 27
    • View Profile
Re: Stirling engine revolution
« Reply #1 on: March 20, 2020, 11:30:38 PM »

Be interested in seeing what you come up with.

Forgive me, and this is certainly not personal, but I have been reading my whole life I can remember about Stirling engines and miracle breakthroughs with them about to change the world. Bit like the endless new engines that weigh 3 Kg, do 500HP and get 196 MPH....  All just around the corner and NEVER happened.

I look forward to all new developments in engines BUT, the only ONE I have ever seen come to reality was the rotary. And now that's gone too.  To me there are sound mechanical and physics based reasons the stirling is unsuitable for automotive and the majority of other power applications despite their merits  and until someone comes along that disproves those beliefs, everything else is the same old hype or yet just another press release mainly aimed at raising investment $$.

I'll believe something new and wonderful has been created when I see it in the showrooms .  :0)

Yes, I have seen the very same thing all the years. Marketing is the main culprit. In the older days stirlings were more complicated in theory and weighed more for the same horsepower of regular automobile engines and so were not competitive. They also took longer to start. Nowdays, with all the emissions BS there is on regular car engines...... NOT SO! Really now, the BS is deeper than ever berore! Modern emissions garbage has made the once complicated stirling cycle look like a toy compared to all the complexity of all various catalytic systems, and for diesels now we add the particle filters, piss injectors, and yet another extra catalytic converter!

Now if we add really modern materials and knowledge to the old stirling concept, what we get is a little like Star Trek. There is a very serious efforts on going with major energy corporations to use thermoacoustic stirling cycle based technology to liquify natural gas, with large prototypes (over 500 gallonsLNG/day) already in operation. The most modern submarines use stirling engines and can stay under water for weeks without nuclear power. Nasa currently uses stirling engines in spacecraft where efficiency and weight are extremely important.

I mentioned the free piston type engine, very simple in construction. Very complicated calculations needed to design.  Only two moving parts, no cranks, or bearings. Pistons are gas floated or magnetic floated. Most efficient of all concepts. The Thermoacoustic concept has NO moving parts but is a little less efficient. About 30%-35% at best, but hey, that's as good as most diesels. Good design principles are always needed, and I see a lot of amateur engineering used for testing these engines, with the expected bad numbers emerging from these tests.

Oh yea, they are also very quite! The reason they are used in submarines. For off grid, electricity is easily, and very efficiently generated from burning wood, or anything else! Refrigeration for food storage and air conditioning is just as easily done with a stirling driving a compressor and a refrigerant, or compound stirling machines and NO refrigerants.

The machine work and shapes are very simple. The dimensions are not simple to calculate if a viable machine is expected. All dimensions and the weights of the two moving parts are very important. Dimensional tolerances will not be extremely tight however. Material choices and assembly techniques (I.E. welding processes) will be very important. Working gas will be extremely important with high pressure helium the best. The best machines will have higher pressure combined with higher hot side temperatures. This is why materials and assembly must be carefully chosen. Just because there are stirling engines that will run on the heat of your hand doesn't mean they are efficient and of any practical use! These are "bait" engines used to draw young people into college engineering programs, for which the other incentives (scholarships) will not be offered the next year and the school will get all your money, which you wont get back because your field of study will be obsolete before you graduate! Yea, the system is broken and a very corrupted racket with loads of greed, a modern day mafia type system.

Also, a well built free piston engine (hermetically sealed system) will last 30 years or more.

I am posting all of this info for all off gridder's out there that need a good sustainable low or no maintenance power source.

Who knows, with this virus stuff going around we might all need to live isolated in the woods like our pioneers did for a while.

scott p

  • Jr. Member
  • **
  • Posts: 80
    • View Profile
Re: Stirling engine revolution
« Reply #2 on: April 26, 2020, 06:52:48 AM »
Strawhat, you have my attention. I will look around to see what is out there concerning the modern stirling. Do you have any references that would make the search more productive?

A theoretical efficiency over 65% is one thing but what would it take for a back woods off gridder working in his shop to achieve that kind of efficiency ?

Thanks for stimulating my imagination.

oldgoat

  • Full Member
  • ***
  • Posts: 153
    • View Profile
Re: Stirling engine revolution
« Reply #3 on: April 26, 2020, 01:04:41 PM »
Further reading
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19880002196.pdf
but I think diesels will be around in the forseeable future.

scott p

  • Jr. Member
  • **
  • Posts: 80
    • View Profile
Re: Stirling engine revolution
« Reply #4 on: April 26, 2020, 06:58:51 PM »
Thanks oldgoat, will have a look later.

Wally mintoís wonder wheel would have be considered a heat engine. I suppose a large diameter wheel might prove practical. With todayís bearings, friction would minimal. Canít get much simpler with only one moving part. Perhaps the directed expansion of a gas flame could be used to help push the wheel along as it heated the container. Throw in some electronics to be used for timing purposes. Who knows might be able to push the thing up to say five Rpm. Torque would your only friend.

scott p

  • Jr. Member
  • **
  • Posts: 80
    • View Profile
Re: Stirling engine revolution
« Reply #5 on: April 30, 2020, 07:55:04 PM »
So it looks like they did build a Stirling engine large enough to be installed in a car. Upside it was more efficient than its gasoline-powered counterpart. But it was not very responsive when throttled. The price of oil was so low and since the impact of pollution was not regarded the engine was not considered to be practical.  Perhaps it is time to take another look.

It seems the stirling is practical at smaller applications.

Concerning the Wally wheel

Unfortunately I didnít see the myth busterís episode concerning the Minto wheel. I did though read the Minto wheel article put out by the Mother Earth magazine.

Bottom line, the wheel turns and it produces lots of torque. I donít know what those back yard myth busters were doing but the Mother earth people put a lot of time and money into their wheel. It turned and it produced plenty of torque at a very low rpm. The mother people stated, I believe, their wheel was only good for one rpm in five minutes. It would be pretty hard to get anything useful out of that.

Wally Minto though, in his book, laid out the theoretical groundwork for developing a twenty-foot diameter wheel and concluded that it would turn about one rpm. Rpm is based on several different factors and is variable to a degree.

In reading his book it was obvious he put a lot of research and time into building his wheels. Other than running his wheel through an automotive rear end or transmission to get higher rpm he didnít say much about going beyond that. He related his wheel to slow speed high torque applications such as pumping water or grinding grain.

As I said before I donít know what the myth busters were doing or what the mother people were expecting.

If the ultimate goal was to generate a high-speed application from a shaft that is turning at one to five rpm they may have been approaching the problem from the wrong direction.

I missed an opportunity to purchase 15-volt wind generator that turned at 300 rpm. I have also seen a web page that demonstrated how to build permanent magnet wind generators. With their methods you can throw as many poles as you want into your generator. Four poles 1800 rpm, eight poles 900 rpm, 16 poles 450 rpm.

The heat required too vaporize a given amount of low boiling liquid such as propane or a refrigerant is not that great. You only need enough to pressurize the tank and force the remaining liquid up to the other container. Wally has a lot to say about designing a wheel.

I am posting the information I have.

If I were to undertake the construction of a wheel the first thing would be to connect a gearbox that could be run backwards. I have a 20 to one box that could be geared to give 40 rpm. I think that might be enough to run a slow speed generator of the required voltage to charge a battery bank. The higher the battery voltage the less amperage required.

Also inclosing the wheel in a sealed well-insulated building and burying a length of pipe in the ground to earth cool the wheel atmosphere. Perhaps an absorbent type of refrigerator could be used to drop cold air into the pipe to create a draft into the structure. Hopefully the draft would be enough to flush the heating portion of the system out side before it could affect the top of the wheel. Perhaps the excess heat could be channeled and vented and perhaps a cool draft would cool it down somwhat.
 
That hypothetical train of thought is as far as I am willing to go.


















scott p

  • Jr. Member
  • **
  • Posts: 80
    • View Profile
Re: Stirling engine revolution
« Reply #6 on: April 30, 2020, 08:04:33 PM »
We will see if this works. I resaved a win.doc to text only.

scott p

  • Jr. Member
  • **
  • Posts: 80
    • View Profile
Re: Stirling engine revolution
« Reply #7 on: April 30, 2020, 08:17:20 PM »
Well, that didn't work very well.

scott p

  • Jr. Member
  • **
  • Posts: 80
    • View Profile
Re: Stirling engine revolution
« Reply #8 on: April 30, 2020, 09:04:14 PM »
This place gives all the information I tried to attach earlier.

Wallace Minto: Freon Power Wheel - Rex Research

scott p

  • Jr. Member
  • **
  • Posts: 80
    • View Profile
Re: Stirling engine revolution
« Reply #9 on: May 01, 2020, 05:43:48 PM »
Thanks for the input glort.

The gearbox I mention is about the size of a five gallon bucket. I would connect it backwards directly to the output shaft of the wheel to get 20 rpm or gear with a chain (again off the output shaft) one too two to get 40.

Anyway enough said about that. I read your PDF file about used veg oil. I have a couple hundred gallons of the stuff I collected years and years ago. It has been so overcooked it is almost black and nothing has settled out of it in all those years.

Would you run stuff like that in your engine? If being overcooked would that radically change the chemical makeup of the oil in a bad way ?