My first post. Advice needed.

[Alfista]

Ian, thank you for the post. I was only offering a possible calculation. I was not in any way disputing your calculation or measurement. Neither was I trying to point to possible losses or inefficiencies. On the contrary, I read about your Stuart engine with interest and it was very interesting to read about your results. I was just stating a possible calculation for the indicated horse power. I know that ihp is completely outmoded but it still seems to serve some purpose in these sorts of discussions. I have learned a lot from reading your posts.

I do not have a lot of sophisticated measurement equipment and so my data is usually rather basic and sometimes reduced to guess work.

I have put together a number of generator sets, mostly using steam engines and permanent magnet motors as generators, but I also have two permanent magnet AC alternators, one is about 1000w max, the other about 1600w max.

From my very limited experience with Stirling engines I am already keenly aware of the importance of minimizing friction. This is no less true in the drive train or transmission. Yesterday, for the first time, I was able to test some sprockets with chain. As one would expect, this system is inexpensive and reliable and frictional losses lie in the middle ground, it is not as friction free as gears or direct drive but has less frictional loss than rubber belts with pulleys. Another nice advantage is that it is so easy to experiment with the ratios and it is easy to find a great variety of sprockets in terms of the number of sprocket teeth. I would add that the engine must put out a certain nominal output for this drive to be efficient, due to the weight of the materials involved and the friction.

It seems that many folks here are interested in micro power production. My best guess about this system is that it would be most useful between about 50w to 750w. I am sure that it could stand up to more power but if I were building it, I would go to heavier chain beyond one or two hp.

[Alfista]

Wellington, if you are able to build an engine that can take advantage of 10 bars of pressurization, I have no doubt that you will easily resolve the relevant safety issues. Let me add that the issue of boiler explosions is generally misunderstood. Of the dozen or so boiler explosions that I have read about, it is very difficult to find one that was not a result of willful neglect or sabotage. Typically, in the old days, an ignorant operator might jam the safety valve shut to get just a little more power, or an engineer knew that the boiler was very low on water but it was just "too inconvenient" to stop. "If I can just make it to the next water station..." Lastly, I will give a quote from K.N. Harris, a brilliant steam engineer : "I would sooner remain in the vicinity of a well made and maintained boiler working at 1,500 psi than a badly made and maintained one working at 50 psi." and " a decently made boiler, well made of good materials, working at a pressure not exceeding that for which it was designed, is as little dangerous as a sewing machine or typewriter." (I paraphrase.)

[Wellington]

Wellington, if you are able to build an engine that can take advantage of 10 bars of pressurization, I have no doubt that you will easily resolve the relevant safety issues.

The truth is I have no clue how to design a 10 bar stirling but would very much like to know. I have access to a tig welding machine which can weld almost any material so thats a good start. I was planning to weld a bike tyre valve into a cylinder and experiment a bit but cannot seem to find any info on the internet on how many bar pressure can be achieved with a human powered bike pump. If you can forward me in the direction of the laymans guide to pressurizing a stirling engine with a foot pump or hand pump or even a micro compressor that would be great. Love steam engines and the bonus of distilled water they output but the perfect complementary technology to stirling engines for me has to be low tech gravity fed diesel stoves with thermocouple overheat shut off valves. Unlike a wood stove or steam engine you can leave a diesel stove burning all night on a tiny amount of fuel and they are not dependent on an electricity supply. I also think Wood gas stoves are a good stirling engine match up or a rocket mass stove if you have room for the mass part.
.Wellington.

[Bumpkin]

Narrow street bicycle tires can inflate as high as 130 psi. That's about ten bar. (The first bar wouldn't show on a gauge.)
Bumpkin

[Wellington]

Narrow street bicycle tires can inflate as high as 130 psi. That's about ten bar. (The first bar wouldn't show on a gauge.)
Bumpkin

Thanks bumkin. So I guess people just stick a bike tyre valve on their engines heat tube to pressurise them and attach a diaphragm at the cold end and I will have a ten bar machine? is it really that simple or am I just wishful thinking?
Wellington.

[Alfista]

Wellington, I cannot give any advice on pressurization but I will give you a couple of good references. I hope that anyone reading this who finds mistakes in this information may offer corrections or the benefits of their experiments. The second volume of James Rizzo's Stirling Engine Manual is mostly dedicated to developing a successful, pressurized, table top Stirling engine. Although I respect his work very much, I have not found his books to be very helpful for this reason: Perhaps if I had more experience as a builder of hot air engines or if I had a greater ability to visualize objects in 3D, then I would be able to take better advantage of his Stirling Engine Manuals. I have built at least a couple dozen engines from scratch or from castings. Personally, I would rather have one or two sheets of well drawn plans than volumes of pictures and talk about the engines. Nevertheless, I recommend the books even at 50 U$S each which is about what I paid for them.

Ross' book on building Stirling engines is a generous guide to the process of building an engine that can be pressurized but again, no real plans ... The Darlington / Strong book on Stirling engines includes a very detailed set of drawings for a beta engine.

It is my impression that building an engine that can take advantage of 10 bars of pressure is a major undertaking, completely worthwhile but probably not recommended as a first or second engine. There are some fantastic builders on this site, Chris_74_fr among them. He recently built a very successful alpha engine, pressurized. I am jealous ! [/size]

[Bumpkin]

Simple and easy are entirely different things. To return to the original premise of a useful engine to add on to a woodstove: In Stirling-engine parlance that's a moderate-to-low temperature heat source, so you need a relatively large engine to process heat in and out externally, regardless of how high-pressure and efficient the engine is internally. A dedicated-burner engine could perform much better, but the only sensible economy would still be cogeneration, where any commercial version would need a custom-built burner certified to modern biomass space-heating regulations. You'd need far deeper pockets for that than you would for engine development. So if you want to make an engine to sell, you most likely need to settle for low-grade heat, where more pressure than is needed to harvest a scant crop might only put unnecessary stress on other parts of the system. My two cents.

Along with following and digesting some of the links you've been given here, you might want to look at stove-top fans for more inspiration/information.

Bumpkin

[Wellington]

Wellington, I cannot give any advice on pressurization but I will give you a couple of good references. ......

Thanks Alfista. I will look up your references.
Wellington

[Wellington]

Simple and easy are entirely different things. To return to the original premise of a useful engine to add on to a woodstove: In Stirling-engine parlance that's a moderate-to-low temperature heat source, so you need a relatively large engine to process heat in and out externally, regardless of how high-pressure and efficient the engine is internally. A dedicated-burner engine could perform much better, but the only sensible economy would still be cogeneration, where any commercial version would need a custom-built burner certified to modern biomass space-heating regulations. You'd need far deeper pockets for that than you would for engine development. So if you want to make an engine to sell, you most likely need to settle for low-grade heat, where more pressure than is needed to harvest a scant crop might only put unnecessary stress on other parts of the system. My two cents.

Along with following and digesting some of the links you've been given here, you might want to look at stove-top fans for more inspiration/information.

Bumpkin

Yeah, red tape is a real pain. Im planning to design an engine to fit an existing multi fuel stove design which has a removable hot plate on top. The idea is to design a small stirling engine to fit in the same hole as the removable hot plate and generate a small amount of power (say 20W) to charge small devices. As far as I know I wont need any permisions but correct me if you think I'm wrong.
Wellington

[Josephkaisner]

Wellington,
I,m just starting in stirling engines as well but one excellent, excellent, book that has helped me a lot is called STIRLING AND HOT AIR ENGINES. It is a must read.

I work with ATVs and i think one of the best alternators that you could get would be the one for the 1988 Kawasaki Bayou 220 and the flywheel. It produces 12v and is very easy to turn. i think that a very small stirling engine could make good power this way.

Joseph Kaisner

[Ian S C]

Joseph, I presume that the book you mention is "Modelling Stirling and Hot Air Engines" by James G. Rizzo.
This book contains most of the information that is in "The Stirling Engine Manual" vol., 1.
A good generator can be made from the DC motor from a tread mill, these range from 1kW to 1.5kW at 200 volts (on the motors I'v seen).
Ian S C

[Josephkaisner]

The book that I was speaking of was written by Roy Darlington from the UK.
do you know where I could get my hands on some of Rizzo's works?

[Wellington]

Joseph, I presume that the book you mention is "Modelling Stirling and Hot Air Engines" by James G. Rizzo.
This book contains most of the information that is in "The Stirling Engine Manual" vol., 1.
A good generator can be made from the DC motor from a tread mill, these range from 1kW to 1.5kW at 200 volts (on the motors I'v seen).
Ian S C

yep, I came across a tredmill at the car boot sale the other week and I cut out the motor. What a great source of DC motors! 750 Watts 230v!. No Tredmill is going to be spared from now on. Note to self: when the zombie apocalipse begins go to the gym. :)
.Wellington.

[Ian S C]

Gyms are important places to hang out at, waiting for someone else to wear out the machines, as well as motors there is plenty of metal work to recycle, although I suppose that the gym rents or leases the gear.
Ian S C

[Alfista]

Joseph,
the Rizzo Manuals are currently available on amazon.com and if I am not mistaken, also through Tee Publishing. Please also see my mini review above. Also, for those interested, you will likely be looking for a low hp, high voltage motor such as a Dayton 4Z524B, 180 vdc at 1725 rpm. .5 hp. High voltage at low rpm !