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Stirling engine revolution

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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.


--- Quote from: glort on March 17, 2020, 01:41:14 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)

--- End quote ---

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:
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.

Further reading
but I think diesels will be around in the forseeable future.

scott p:
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.


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