Time for another ‘rebirth’ of the Stirling Engine ?

[Michael GilliganParticipant @michaelgilligan61133]

This article from 1969 makes interesting reading:

https://hagenbeuk.nl/wp-content/uploads/2021/05/1969RebirthStirlingmotor.pdf

MichaelG.

[Andrew CrowParticipant @andrewcrow91475]

A very interesting article  Michael, unfortunately the research seems to have dried up sometime in the 1970’s. I seem to remember reading somewhere that they were considering Sterling  cycle engines for electricity generation on the Moon using solar power as the heat source. The development and considerable improvement of solar panels for producing electricity was probably responsible for its demise.

However, it doesn’t prevent us from having a lot of enjoyment from making them.

Andy.

[David AmbroseParticipant @davidambrose86182]

The Swedish navy use Stirling engines in their submarines to provide an air-independent propulsion system.

[Nigel Graham 2Participant @nigelgraham2]

It is interesting… both in itself and in whatever happened next.

 

That paper was published nearly 56 years ago, so do we know if any further development took place?

One or two may question the exhaust claim: yes that engine burns all the fuel to carbon-dioxide but..

“Machines producing cold”? Really? Heat can be generated and removed, but producing cold generated? We can see what the author meant – reducing temperature – but it’s an oddity in a scientific paper.

I wasn’t aware that 19C boilers were made of cast-iron, although boiler explosions did occur sometimes, a few by design or installation flaws but most from operators’ neglect or error.  However, the authors were citing what Robert Stirling observed when heat-engines were in their infancy; not their subsequent, rapid developments and increasing safety in boiler design and operation.

 

Even if not personally hot-air engine builders we all know and appreciate the miniature ones that grace the exhibitions, or tick cheekily over on unlikely heat sources. Their commercial big brothers fell out of use with the i.c. engine and electric motor, but have been revived for specialist applications. E.g.:

https://www.jafmonline.net/article_1273_eb185b7e8703f4cb74a806b6d333c61b.pdf

This paper, in the Journal of Applied Fluid Dynamics‘ on-line edition, covers the principle and thermodynamics of the engines, then summarises developments and applications from 1816 (the original Stirling engine) to almost present (the paper is dated 2011).

Notably, it includes perhaps the first use of solar power, by Ericsson in 1883. A curved reflector perhaps 4m X 3m judging by the man included for scale in an engraving, was line-focussed on a heat-exhanger; but tantalisingly the picture and text tell us no more than that. It is not clear how the reflector was kept facing the Sun, but this was probably an experiment rather than production machine. The illustration is not a photograph but a perspective drawing that might not represent the shape very closely. However, it seems not parabolic but one that kept the linear heat-exchanger irradiated in its fixed elevation for a few hours.  Maybe the man’s role was to tweak it round every so often…

….

{On solar power, my brother built a solar PV array on an outhouse roof at their home near Glasgow. The array is only about 1m square, but inclined to correct angle for latitude, and on a turntable whose low-wattage motor clocks it round for maximum azimuth irradiation. It feeds storage batteries and associated electronics, to supply the house.}

[David Ambrose]

On David Ambrose Said:

The Swedish navy use Stirling engines in their submarines to provide an air-independent propulsion system.

Indirectly via charging the main batteries. The small Stirling engine units can run underwater, using liquid oxygen, and are virtually silent. They extend the submerge time from about 3 days using the noisy main diesel engines to about 3 weeks using Stirling’s.

Phillips had stirling powered buses running around Amsterdam years ago. But the Stirling is not suited to the highly varied speeds and loads of automotive use.

[FulmenParticipant @fulmen]

It’s the liquid oxygen that provides air-independence, you could run a diesel on the same oxygen. The real benefit of the stirling engine is high efficiency coupled with low noise signature. IIRC they even compress and store the exhaust.

[paul rushmerParticipant @paulrushmer83015]

Have any of you read The Star Drive by Phillip Hills sub title the true story of a genius, an engine and our future? I found it well written and reaserched in it he talks about KRUSTY Kilopower Reactor Using Stirling Technology built by NASA in 2018. This is a small nuclear reactor running eight free-piston stirling engines the whole thing about the size of a dusbin it is to be used to power future expoditions

Paul

[duncan webster 1Participant @duncanwebster1]

I once read a proposal to have gas central heating boilers with built in Stirling engines to generate electricity. Seemed quite sensible as what would otherwise be waste heat from the electricity generation kept you warm. It never took off, probably too expensive

[BazyleParticipant @bazyle]

Anyone had their hands on one of the gas central heating boilers that contained a stirling engine to provide 1kW that had a brien flurry of publicity 20? years ago.
Another small commercial use is in little generators in buoys to light a warning lamp using gas stored in the body of the buoy. Are they still used given the advances in batteries and solar panels?

[John HaineParticipant @johnhaine32865]

The Stirling buoy generators were particularly interesting as they had no rotating parts.  Power and displacer pistons were both mounted in diaphragm so were resonant and coupled so they oscillated in quadrature, the power piston having a moving coil to generate the electrical power.  I once worked on a feasibility study for microprocessor controlled gas cookers, problem was power when people expect them to be independent of the mains. One idea was to use one of these to make it mains independent. Then the client pointed out that to meet regulatory standards at the time a pilot light had to generate the BTU equivalent of 500 watts, so a 1% efficient thermopile could easily keep a battery topped up. Nowadays of course wasting gas keeping a flame alive continuously would not be viable.

[John HaineParticipant @johnhaine32865]

It’s also not well known that if you drive a Stirling cycle engine “backwards” it can act as a refrigerator, and indeed these are used to achieve cryogenic temperatures in a very small space. There was a company that spun out of Sandia National Labs in the USA that I once visited which had a superconducting filter for cellular base stations to solve a specific problem in US networks. This was a tiny package with 2 sma connectors built in to the top of a refrigerator the size of a large vacuum flask, say 450 X 150 mm.  The fridge had a vibrating diaphragm Stirling arrangement driven from 60 Hz that could generated suitable low temperatures in a small volume for the filter, which was fabbed using thick film technology. No need for big cavities when the conductors have zero resistance. Similar coolers are used in various sensing applications and I suspect this is the main application of the Stirling cycle these days.

[John Haine]

On John Haine Said:

It’s also not well known that if you drive a Stirling cycle engine “backwards” it can act as a refrigerator […]

This is quite a good overview:

https://www.ricor.com/wp-content/uploads/2019/05/Ricor-Stirling-Machine-Basics.pdf

MichaelG.

[John Haine]

On John Haine Said:

The Stirling buoy generators were particularly interesting as they had no rotating parts.  … Nowadays of course wasting gas keeping a flame alive continuously would not be viable.

Gas powered buoys have an interesting history.  In the 19th Century, they exploited Acetylene burning in air because it  gives a bright whitish light.  Acetylene lamps were very common, and are still used occasionally today.   The Acetylene was safely generated by dripping water on to Calcium Carbide. Unfortunately replacing Carbide at sea was irksome in itself and failed if the Carbide got wet during the transfer.   So they switched to Acetylene compressed in a cylinder.  Weight for weight much more light than Carbide, so fewer trips needed to change cylinders, and wet wasn’t a problem.   Wonderful, except it was found that compressed Acetylene can explode by polymerising spontaneously!   Many nasty accidents.    After much research Acetylene was tamed by dissolving it under pressure in Acetone, which is how we store it today.   Still have to be careful with Acetylene, especially if a cylinder has been in a fire.

Back to Stirling engines, I think “rebirth” is the wrong word: they’ve never gone away.  Whether or not they’re used depends on the requirement.   All technologies have pros and cons and Stirling engines face stiff competition that changes over time.    In Victorian times Stirlings were common in small workshops because they didn’t need a dangerous high-maintenance boiler.  Not used in bigger factories because a big centralised steam engine driving a line-shaft system was cheaper.  Both edged out by a better solution, which is electric motors.    Today IC engines have a better power to weight ratio than Stirlings on earth, which is important in vehicles.  In outer space though, Stirlings win, because IC guzzles air which is in short supply is a spacecraft`.     Used in submarines because they are much quieter than IC, for cooling, and anywhere else their characteristics suit the job.

Anyone built a Stirling powered model locomotive?  No need for a boiler or boiler inspector.   I guess not because they’re caught between three good alternatives:

• Not as drop-dead sexy as a live-steam loco.  (I love ’em)
• Not as powerful, easy to build or as low maintenance as an IC, their problem being nasty noise and smell.  Unlovable!
• Not as powerful, easy to build, low maintenance or as easy to drive as a quiet high-torque electric loco, the disadvantage being charging the battery.

Re power to weight, ages ago I built a Jan Ridder’s Coffee-cup Stirling and measured it’s power output with a home-made torque dynamometer and Arduino.  From memory, either 0.2W or 0.02W on the shaft.   I think the lower figure.   I make no apology for the rough construction – this is an experimental engine.   Well-made where it matters – bearings, piston, cylinder, and that blob of green plasticine is carefully weighed and positioned to balance the flywheel.

An extreme worst-case example, but  a power output of 0.2W (if that) from an engine weighing 533g ain’t good when an automotive diesel produces about 6700W per kilogram.   On the other hand,  the Coffee-Cup engine spins impressively on a mug of hot-water!

Dave

 

[Nigel Graham 2Participant @nigelgraham2]

I have several first-half 20C engineering text-books for their help in trying to replicate old machinery.

One does go into hot-air engines, heat-pumps, refridgerators and compressors; all related thermodynamically. It uses as an example a theatre installation where the heat-pump warming the auditorium in Winter, becomes its cooler in Summer. No refrigerant is necessary; the heat transfer is simply to or from the air passing through it, by compression or expansion.

This was driven by an oil-engine, and the text gives the calculations showing this particular plant is significantly more fuel-efficient than if the oil were burnt as heating-fuel directly. (The corollary is too obvious to mention.)

That was in the 1930s, I think.

[renardiere7Participant @renardiere7]

I’d like to thank Paul Rushmer for his recommendation of Pip Hills book “The Star Drive”. I picked up a brand new copy in hardback for £3 delivered from Abebooks which arrived this afternoon.  I’m well through it already, what a superb book! Thanks again Paul.

[Howard LewisParticipant @howardlewis46836]

I thought that not too long ago, large (comparatively) Low Temperature Differential engines were used to pump water from rivers in remote areas of countries, such as in Africa.

The whole machine was launched into the water, with the water acted as the cold source, and the sun as  the hot source.  The resulting energy was sufficient to pump water “ashore” to irrigate fields, basically using solar energy.

Even longer ago, Phillips used Stirling engines to to drive small generators for small unattended transmitters in remote areas.

The Stirling engine powered central heating units were made by a New Zealand company, “Whisper Gen”. The gas provided both heat for the house, and energy to power a linear generator which provided electricity for the house. The principle was an oscillating magnet generated current in a static coil which fed the house.

Used in conjunction with PV panels, and a battery storage facility; cheap electricity should be available year round.

Howard

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