Stirling Engine Q&A Q1-Q50


To Japanese Page


Q&A from May, 1996 to June 9, 1997.


Q50: Does the displacment piston in the displacment engine touch the cylinder walls?
9 June, 1997
knight_01@hotmail.com

A50: In the case of most of the model Stirling engines, the displacement piston does not touch the cylinder wall. The woking gas flows between the displacement piston and the cylinder wall. On the other hand, in the case of the real Stirling engine, the seal device (piston ring) is used at the displacement piston. Then almost of the working gas flows in the heat exchangers.


Q49: My profession is mechanical engineering (design engineer),and I like your web site very much. I found this site looking for ideas to a small contest we're going to have on our company.
My questions are:
Is it possible to use the "LSE-01" model to run a small vehicle, 10m on plain ground?
Is it possible to use the "LSE-01" in a horizontal position, and not vertical as in your picture?
Is it strong enough to give good acceleration?
5 June, 1997
Ronney Tollbom

A49: The LSE-01 has too small power for the vehicle, maybe. I recommend that you reform the engine to more larger size or the multi-cylinders type as you said. The LSE-01 is designed to aim at easy building. When it is used as the competition engine, I suggest following changes.
(1) More thin and light heater cap is required. (--> 0.5mm thin or less)
(2) In order to keep a high compression ratio, more short distance between the hot and cold cylinders is required. (--> 20mm or less)
(3) More light flywheel is required. The flywheel in my plan is too enough.
(4) More large cylinder bore is better. (--> 15mm)


Q48: First time to your site, nice and to the point. like the q&a column. I am in charge of a diesel truck shop near San Francisco and verry interested in solar sterling engines and large scale engines. keep up the good work!
1 June, 1997
George Booth

A48: Thank you. Yes, I keep my work.


Q47: I have heard the mechanical efficiency for estimation the shaft power of the Stirling engine. How can I estimate the value of the mechanical efficiency?
30 May, 1997
Japanese student

A47: It is difficult to estimate the mecanical efficiency of the model Stirling engine. A few years ago, I got the experimental result which the mechanical efficiency was about 30%.


Q46: Please tell me the calculated method for the overlap volume of the beta type Stirling engine.
27 May, 1997
Japanese student

A46: I answer this question in following web page.
http://www.bekkoame.or.jp/~khirata/overlap/overlape.htm


Q45: I hope that some day you will explain details of stirling engine's basic.
22 May, 1997
OkBae Kwon

A45: Yes, I will reform my web site under your suggestion.


Q44: I am building a displacer type Stirling engine. I don't know how many size is the length of the displacer piston. The displacer piston bore of my engine is 42 mm, and the stroke is 30mm. The engine is used hot water asthe heat source and have air cooling.
21 May, 1997
T. Ueno

A44: The length of the displacer piston must be decided by the type of the heatsource and the structure of heat transfer parts. Your engine has a longer stroke, 30mm, then I think that the length of the displacer piston must be decided two or three times of the stroke.
I explain about a heat conduction loss caused by the length of the displacer cylinder. The heat conduction loss, Qcond (W) is calculated by next equation. Qcond=R(Twh-Twc)(A/L)

R: Heat conduction ratio of cylinder wall (W/m2K)
Twh: Temperature of hot side cylinder wall
Twc: Temperature of cold side cylinder wall
A: Section area of displacer cylinder
L: Length of displacer cylinder

In this equation, you see the better size of the length of displacer piston and cylinder.


Q43: I have finished my rotary sterling engine and it runs very well. I used the 90 degree timing factor as you suggested. The engine runs at about 60 rpm and requires a lot of heat. I have used a very effecient cooling system but there is no seperation between the hot and cold sectors (top and bottom because the roter housing is turned from one piece of bronze. I am not happy with the performance of this engine because it has neither rpms or power. The engine measures about 5.5 inches long and has a rotar that is 3.5 inches in diameter. The power piston is .900inch. On the first version I made I used a steel tube for the rotar basis but found that by the time the displacer shoe was added the weight was hard to balance. With that displacer rotar installed the engine ran fine but at only 60 rpm. I thought that the weight may have been too great so I made a second rotar from thin wall aluminum tube and welded end caps on with the center elyptical arc. This rotar only weighs about 8 ounces compaired to the steel one at about 3 pounds. To my surprise the engine ran at the same speed as the steel one but the heat soak on the rotar is much greater. I want to build a powerful pressurized engine next What do you suggest and where can I get information.
Thanks very much Lyle Hudson From North Idaho College
17 May, 1997
LYLE HUDSON

A43: Thank you for your interesting information. It is very useful for many Stirling developers. My rotary Stirling engine has a low engine speed and a few power like yours. It is difficult that the rotary type engine gets high performance. In my opinion, the engine is required follows points.
(1) High temperature difference between the hot and cold sides is required. A construction of the rotor housing must be changed.
(2) High heat transfer is required. I think that the heat transfer area of this engine is too small. Especially, the pressurized engine needs more larger heat transfer area.
(3) Suitable regenerator is required. In order to get a high efficiency, the regenerator must be needed.
Please tell me the information, when you complete to build your new engine.
I hope that you succeed the powerful and efficient engine.


Q42: Do you have any information on solar powered sterlings ?
I hope to build one using a one meter or larger parabolic dish, possibly an old satalite dish. I hope to use it to generate electricity. Please e-mail me any responce if possible.
9 May, 1997
Steve Rollert

A42: Sorry, I don't have any useful information. I have not developed the Solar Stirling engine yet. There are many useful information in the following web site.
http://solstice.crest.org:80/renewables/dish-stirling/
Sandia National Laboratories, USA


Q41: I am a highschool student who is always looking for a new way to power generators and pumps for little money.
I saw a movie that gave a brief summary of these engines and my teacher thought it would be a great project for me. I was just wondering if these engines could be enlarged to power a generator or pump efficently, or if it would even run any thing at all.
I will write back with better questions when I learn more about these engines.
7 May, 1997
Alex Turner

A41: Please contact me again, when you get any good idea.


Q40: You have an excellent site! Ive noticed your mention of both high temperature and low temperature types-but has anyone ever tried to combine them into a compound engine, like the compound steam engines?
I mean the type where the exhaust from a small high pressure cylinder is used as the feed for a larger low pressure cylinder. Do you think this would work in a stirling type?
30 April, 1997
Joel Monka

A40: I think that the high- low temperature combined Stirling engine has good performance. I have heard such idea but not seen it yet. Generally, the low temperature Stilring engine has a low efficiency. Then the combined engine system is not suitable for the practical use. In my opinion, the high temperature Stirling engine must be used as a power source of a high efficiency system. The low temperature Stirling engine must be used with natural heat source like solar.


Q39: Thanks for the wonderfull web-site on Stirling Enginies. I was interested in the Stirling Engines and after visiting your home page I decided to build my first model.
I started with the Can Stirling model. The engine is not running and I have these questins:
1) Do I have to struch the palloon or do I have to make it little bit loose?
2) Can't I use the fishing thread to make the hole in the palloon, so that it is air tight?
3) what do you do with the problems that: the paperclip moving to the sides and that the cran (i.e. the wire) is coming out from one side of the wood-frame?
4) my steel can is 13 cm hiegh and the piston is only 6cm hiegh, does this have any negative effect?
28 April, 1997
Abdirahman M. Omar

A39:
1) You must struch the baloon somewhat as a face of the baloon becomes flat.
2) I used a needle to make the hole. And I could get a few air leakage when the machine oil was droped.
3) This engine has a low engine speed. Then above probrems are not important, I think. I did not manage for them.
4) It is no good. When you use the 13 cm steel can, you must set the piston height to 9cm. It is important that the dead volume in the engine is decreased.


Q38: I now have a new computer that will help me get some of your plans on the next model I plan to build. I have 2 each 20 cc glass syringes. I am concerned on cutting them. I see you mention using a green cutting wheel. Is that a wheel that is used to sharpen carbide tool bits?
I want to make sure before I continue.
23 April, 1997
Larry A. Boreham

A38: Yes, the wheel is used to grind the carbide tipped tools. Please grind the glass syringe slowly without a force of your hand. It is better that you are turning the syringe, when you grind and cut it. If you fail to cut the syringe, it is not my fault(^^).


Q37: I am a mechanical engineering student investigating oil transport along the Stirling engine's trunk pistons. Do you have any information about this subject, or could you tell me where to find it.
17 Aprol, 1997
Ronald Stultiens

A37: Sorry, I don't have useful information of this subject.


Q36: I am a student at North Idaho College. I am a machine tech student. I have built several stirling engines. The last one a is a rotary style like the one I saw on the web page by Koichi Hirata. I have just finished this engine and I am about to start it.
My question is are you informed about the timing of the rotar/displacer to the power piston timing. Another question I have is about the ratio of displaced volume I think you call it swept volume between the rotor and the power piston. We have been using 2:1 ratio for all our engines and it seems to work. Just a note about our findings regarding power pistons. We have been using Graphite as the piston and Glass from a cut test tube as a cylinder. This is the first time I have visited your site and like it very much.
13 April, 1997
Lyle Hudson from NIC

A36: The prototype of my rotary type Stirling engine has 90 degrees phase angle between the rotor and the power piston. Please see
http://www.bekkoame.or.jp/~khirata/gif/rot_str.gif.
I have only tried this timing yet. But another timing is better, maybe. Because the rotary displacer moves the heat energy by the rotation of the heated rotor. Then the most hottest point is moved to the direction of rotation from the heated point.This is not 100% sure.
As you said, my rotary type engine has too large swept volume ratio, maybe. The value is about 15:1. This value does not have any basis. I had built two rotary type engines which cannot run before I completed the running engine. At that time, I thought that the heat input or temperature difference was not enough for the output power. And I increased the swept (displaced) volume gradually. I don't know it was the best selection.


Q35: In regards to the questions about the use of stirling engines in automobiles, NASA Lewis research in Cleveland, Ohio, USA did research with a stirling engine in a truck. The results seemed quite favorable. I believe the source of their engine was a Swedish company, although I do not now recall the name.
3 April, 1997
Martin Meyer

A35: I don't know about this information. The Swedish company was Stirling Thermal Motors, maybe. It is not 100% sure.


Q34: Hi I'm a mech eng student and i'm looking for some expermental data on the performace od stirling engines. Could you please point me to some where i can some info on this.
2 April, 1997
Karl

A34: I have prepared a sample of the experimental data on my site, though I don't know if it is useful for you or not. Please connect to;
http://www.bekkoame.or.jp/~khirata/ecoboyn/exper.htm.


Q33: I am a mechanical engineering graduate student working on stirling engines for a project. I am specifically interested in in modelling of the regenerator.
Do you have any information on regenerator performance models that may be of use to me?
16 March, 1997
Mark W. Holsbo

A33: Sorry, I have not prepared the information about the modeling of the regenerator yet.


Q32: Thanks for this excellent pages!
I'm interesting about ressources for calculating low-temperature Stirling engines. Can you help me. Many thanks.
28 February, 1997
Andi Fuchs

A32: First, I recommand to use the Schmidt method for the calculation. It is an simple isothermal model for the Stirling engine. If you want to an explanation of the method. Please contact to;
http://www.bekkoame.or.jp/~khirata/schmidt/schmidt.htm
Next, I think that you must consider a pressure loss in the regenerator, because it affects the performance of the low temperature Stirling engine strongly. Sorry, I have not prepared any explanation of the pressure loss yet.


Q31: We are two students from holland.( 19 years old ) We must make a stirling engine for a physics school-project ( highschool-level )
We have decided to build Peter Tailler's engine.
Are you familiar with this engine and if so, can you give us some hints e.g about the building of the engine (materials, beginnerserrors). How can we increase the efficiency.
Thanks in advance for helping us out.
20 February, 1997
Sabih Demougin & Rinke Hamers

A31: Sorry, I don't know the Tailer's engine well and I have not build it yet.
In my opinion, the engine must have a few mechanical loss like a model Stirling engine. And the engine have high efficiency when there is enough temperature difference between the hot and cold heat sources, maybe.


Q30: I have just started a project at Staffordshire University invesigating the possibility of using a Sterling Engine to power a family car.
My question is has such a project ever been attempted before, if so is there any technical infomation available on subject.
6 February, 1997
David Dalley

A30: I have heard about four projects for the automotive Stirling engines.
(1) Philips, the Netherlands
A refference is a book entitled "The Philips Stirling Engine."
(2) DOE in USA
Automotive Stirling engines named MOD I and MOD II are very famous. A refference is;
Automotive Stirling Engine Development Project
(3) Aisin Seiki Co. Ltd., Japan
This 30 kW Stirling engine moved a family car with 100 km/h speed.
Sorry, I don,t know a refference in English.
(4) The TEM Foundation at Lund University, Sweden
A refference is; Development of the TEM Stirling Engine
Proceedings of 7th International Conference on Stirling Cycle Machines
November 5-8, 1995, Tokyo
C. Schroder, L. Erlandsson, T. Lia
The TEM Foundation at Lund University, Sweden


Q29: We are interested in information about sterling engines, and we need the addresses of the producers and the distributors (for R+D).
6 February, 1997
Joachim Wacker

A28: It is difficult that I answer your question.


Q28: Greatly enjoyed your site. In the early 1970s I became interested in hot air engines at a time very little information was easily obtainable. I compiled a small, simplistic booklet describing the engine type and the major variations for neophytes. It included an extensive bibliography. I still have several in hand. It is totally out of date, but might be of interest. My personal interest has lapsed for several years, but I am encouraged by the recent work I have found on the web.
10 January, 1997
Tonu Aun

A28: Thank you!


Q27: I made a model engine based an one done by a person named Tailer. Consists of two coffee cans which are the hot and cold tanks connected by a copper tubing. Inside each coffee can is a coke can with a rod attached to the coke can and an above pully wheel. When I heat the one coffee can, I can't get the engine to work. Do you have any suggestions as far as troubleshooting to get it to work? After I fill each tank with water up to the copper tubing inside the can, why does suction of water occur when I moved the coke cans and pully wheel?
10 January, 1997
Doug Weimer

A27: I was looking for a information of the Tailer's engine. But I could not find it. I cannot understand the engine yet. Where can I find them? Is there the information on the internet?
If the engine is a kind of 2-piston-type Stirling engines, I think that a gas leakage is most important. Please make sure that the pistons compress like a gas spring. If the engine has no gas leakage, please decrease a friction loss of the engine mechanism.
Sorry, I have misunderstood the engine, maybe.


Q26: I thank you for the excellent research you have done.
I plan to build a model based on your rotary displacer.
How did you decide on the swept volume of the displacer, Vd?
Would more volume be better, if the displacer was drilled with holes for balance?
I assume that the swept volumes of the displacer and power pistons should be roughly equal.

Vp=Vd {for high temperature heat source}

Again, thank you very much, keep up the good work!
13 December, 1996
Ehben Eliot

A26: In my opinion, if the performance of the heat exchangers are enough high, the swept volume of the power piston and that of the displacer must be same value, as you said. But my rotary Stirling engine has very bad heat exchangers. Then it is difficult that the engine has enough temperature difference between a hot space and a cold space. I decided Vp< If you have any good idea, please try them.
I hope you can develop a new type rotary engine.


Q25: Where can I purchase a working stirling engine? My interest is in a displacer type rated in the 10 to 20 hp range.
4 December, 1996
David Johnson

A25: Please see A24.


Q24: Thank you for such and informative well designed page. Could you give me any information on the availability of commercial engines available in the range of 20 to 40 KW of output.
1 December, 1996
Brian Burt

A24: Sorry, I have not ever heard the high performance Stirling engine for commercial use. Please look for Stirling companies on Other Stirling engine web sites.


Q23: We are a pair of final year mechanical engineering students at the university of strathclyde, in Glasgow, Scotland.
For our project we aim to construct a model stirling engine capable of sustaining powered flight of a R.C model glider or similar aircraft. We are dropping you this line to find out your opinion about this project. I deally we want to use a preasurised heleium engine, producing approx 56W/kg engine weight. We would appreciate any hints or tips you could give us. We know that this R.C flight has been achieved before by an american in 1988 with marginal sucess.We do not know of any other more recent attempts to better this.WE look foreward to hearing from you and congratulate you on an excelent page.
11 October, 1996
martin banks

A23: Thank you for your e-mail. I am very interested in your project.
As you know, the American Stirling engine for the R.C. flight has 56W/kg engine weight (20W/0.36kg) with 1400rpm(23.3Hz) engine speed and 0.25MPa crank case pressure. I seem that this engine is very high performance as model Stirling engines. I have not tried to design the engine like this light weight engine. In my opinion, the engine needs a high performance seals in order to keep the high engine speed. You must sellect or develop the seal mechanism wuth a few mechanical loss like a mechanical seal. I think that this seal is the most important. And you need a piston-cylinder seal with high leakage performace. In the case of the small engine, a few leakage between the piston and cylinder causes a big buffer space loss.


Q22: dear sir thank you for keeping the faith of clean, alternate, power sources. from what i can glean from your material there is a future for the sterling power systems. i was particularly impressed at the potential of hybridisation with solar and natural gas [either propane or methane] preferably methane as propane is heavier than air, will not hold a marker agent [such as mecaptin as used to identify methane] further methane is renewable and is already piped into most us cities and towns.let us hope that the powers that be see the fuelishness [tee hee] of nuclear and caol and begin pursueing a sane path to energy sources. this probably will result in a grassroots interest from small municipalities that cannot afford the ever increasing fuel costs.this same type of movement has resulted in thousands of vehicles being converted to running on cng [compressed natural gas ie methane] with a benefit of ecology and economy. i pray ! that the net is used to raise the conciousness of the masses and that you and your ilk continue with ever increasing success. may the light guide and pritect you all. sincerely aztech in texas
30 September, 1996
aztech in texas
Q21: Please explain what is free piston stirling engine and how it's work ?
19 September, 1996
Tarachan Chantana

A21: I made a web page about the free piston Stirling engine. Please contact to "Free piston type Stirling engine".


Q20: First, I must complement you on your fine pages on an interesting topic, and excellent drawings.
Then a tip: I see most of your costs are for ball bearings.
Nowadays old floppy and hard disk drives are thrown away in large numbers. They have ball bearings of a fairly high quality. The hard drive spindle bearings are also sealed in most cases. Make sure they gets thrown in YOUR wastebasket!
Older 3.5" floppy drives sometimes have _very_ small ball bearings on the driving "crank".
The 5.25" drives are also a good source of 3-5mm axles. They're used as rails for the head assembly.
19 August, 1996
Einar Sjaavik
Norway

A20: Thank you for your information!


Q19: Firstly this is one of the most informative web sites that I have ever visited. I saw it advertised in the rec.craft.metalworking.
I Really like the drawings And my favourite engines are the variable phase model and the Philips Portable power supply My main interest in the Stirling engine is to build a solar powered electricity generator.
Do you have any further information ?
13 August, 1996
Colin Morton
Western Australia

A19: I don't have any useful information about the solar powered electricity generator. I have not try to build it yet. I introduce two web sites. You maybe have visited them already.
Sandia National Laboratories
Bomin Solar Company
Which do you want a high temperature engine like Sandia engines or a low temperature engine like Bomin engines?
In my opinion, if a solar generator using the low temperature engine is built, I think that the cooling system of the engine is very important. The low temperature engine has a low efficiency. It means that the engine is needed to reject a lot of heat. The Bomin engine is used a water pump application, not the generator. I think that the choice is better.


Q18: I want to thank you for the great information on the sterling engine. I am retired and just getting ready to try out your simple engine first. I thank you for very informative data.
27 July, 1996
Larry Borham

A18: Thank you very much!


Q17: Do you have any sources of computer or engineering simulations for Stirling design?

Have you tried model Stirling heat pumps, ie. driving the engine mechanically to drive heat from low to high temperature? Could such devices be used to replace flourochlorocarbon-containing refrigeration systems?
31 July, 1996
JJ Robinson II
http://www.flash.net/~mkia1
USA

A17: Yes, I do. I have and use several sources of the simulations. One is a program of an isothermal model made by Microsoft Visual Basic 4.0. It is a very simple model for Stirling design. Another is an adiabatic model in order to analyze the Stirling engines. It is a very complex model and needs to input many detail informatin of the engine. But I do not use these simulations when I design most of my model Stirling engines. I use only my feeling for them.

No, I have not yet. I think that the model Stirling heat pump needs an enough regenarator and a pressurize working gas in order to get the high performance.
I don't know about Stirling refrigerator system well. Sorry, I cannot answer this question.


Q16: Yours is an excellent page. Good details. Keep up the good work! I hope that some day you will post details of bomin engine. Best wishes.
12 July, 1996
Hassan
New Zealand

A16: Thank you very much!


Q15: How much power does a Sterling engine have? Do you sell any of your engines? If you do, how much?
8 July, 1996
Muhammed-Jamil Galadima
Korea

A15: Many of my model Stirling engines introduced on my web site have about 1W output power or less. A Stirling engine 'MSE-02' for an amphibious ship has 5W output power. In other hands, several practical Stirling engines have 30kW or more.
I have built my model Stirling engines as my hobby not business. I do not sell my engine.


Q14: I has maked the better engine than the first, you has learned a little part about displacer engine, and it run better and more strong. compression pressure are at 0.6 kg/cm and pressure from heater volume are at 0.2 kg/cm in displacer cylinder. It run at 800 rpm. It's made for demonstration for my friends and other people. I has tried to make 2 piston engine Stirling but it run not because engine has too hight compression pressure and difficult starting. Maybe for little flywheel or for little volume in cylinder. All are ballbeared. Want to listen from you.
26 May, 1996
JENS EIRIK SKOGSTAD
Norway

A14: I think that the engine has not able to run by too high compression pressure. I seem that a heater volume or a heat input is not enough. I recommend that you chnage a phase angle of the engine to more 120 degree. The engine will get more heat input by the big phase angle and you will be able to start it easily.


Q13: The Bomin low temperature difference engine design appears interesting. Have you considered designing a model of their engine? I'd also be interested to hear from you an explanation of how the displacer cycle is started apparently by a valve that opens at a certain pressure and maintained automatically.
24 May, 1996
Jim Linder

A13: I have not built the low temperature difference engine. But I know that there is the model engine operated by only 10 degrees Celsius temperature difference. I introduce two web pages for more information.
Palm Top Stirling Engine of Saitama University
Low Temperature engine of Magic Motor Company
I am very interested in the automatic starting system. But I can not devise the system yet. Is there someone who has devised the system?


Q12: Information about our fuel oil burner: fuel oil burner, power 5 kW, NO2 < 120 mg/Nm3 3% O2, CO < 80 m/Nm3 3% O2. The burner use fuel oil (in german we say also "diesel" or Heizoel extra leicht). The output power is 5 kW. It is only a burner. After the burner you have hot exhaust fumes with a temperature from 300 to 500 C. The burner is developped for hot water heating systems. But we will use it later for a stirling engine. Please send me a principle picture for what you will use the burner.
23 May, 1996
Urs Loepfe
Switzerland

A12: I present a picture of a combustor for a Stirling engine. The combustor is here. This combustor has been used a 100 W class Stirling engine 'Ecoboy-SCM81'. Propane gas is used as the fuel. The air for the combustion is heated by the exhaust gas in order to keep a high efficiency.


Q11: Is there any way to test the efficiency of a model engine to predict what a full scale engines performance will be?

A11: No, I have not test the efficiency of the model engine. Many of my model engines are built without the consideration of its efficiency. If the model engine is built with the consideration, I may predict the efficiency of the full scale engines reffering that of the model engine.


Q10: Have you ever wanted to build a large scale Stirling Engine after seeing a certain model engine that you built run well?

A10: No, I have not. I think that the large scale engines have different structures compare with the model engines. For examples, there are complex heat exchangers , seal mechanisms, strong crank mechanisms and et al in the large engines. But the model engines are useful for designs of the large engines. The model engines have a lot of wonderful ideas and I can realize them easily.


Q9: Does the pressurizing act like a flywheel that stores kinetic energy?

A9: No, it dose not act like a flywheel or a gas spring. The pressurized Stirling engine needs more bigger flywheel. Because an amplitude of the pressure vibration increases.


Q8: Why are large Stirling Engines pressurized?

A8: There is an equation of ideal gas.
P x V = M x R x T
(P:Pressure, V: Volume, M: Mass, R: Gas constant, T:Temperature)
The pressurizing of the Stirling engine means that the mass of the working gas in the engine is increased. As the result, an amplitude of the pressure vibration increases, and P-V diagram becomes large. Of course the area of the P-V diagram equals to the indicated power of the engine.


Q7: How much does your average model engine cost to build?

A7: The cost of my easy type model engine is about 50 US dollars. Half of them are costs of miniature bearings. Usualy I use 6 bearings in the easy type engine. The cost of my model boat is about 400 US dollars. Sometimes I use them the miniature bearings over 30! And I buy R/C (radio control) system for them. I think that the miniature bearings are very expensive to build the model engines.


Q6: In the case of the displacer type Stirling engine, do you deside the value of displacements and other features?

A6: For the displacer type Stirling engines, I think that their bore/stroke and the swept volume of the displacer piston/the swept volume of the power piston are very important. First, the swept volume of the power piston, Vp must be decided by the demanded output power. The bore/stroke of the power piston is not important. Because these value do not affect the working gas flow and the heat transfer in the engine. I think that you must decide these value by the feature and the mechanism of the engine. But I do not like a long stroke type engine, because It has larger mechanical loss than a short stroke type engine generally. Second, the swept volume of the displacer piston, Vd is decided by the type of the heat source. If there are enough heat and high temperature heat source, Vd must be decided as small as possible in order to keep a high compression ratio and I will decide Vd/Vp=1. Other hand, if poor heat and low temperature heat source is used, Vd must be decided the enough volume for accepting the poor heat input. When I use a low range temperature heat source (as the hot water), I will decide Vd/Vp>10~20. Third, the bore of the displacer piston is decided by the type of the heat source too. If the low temperature heat source is used, the bore must be decided a large value in order to keep up a wide heat transfer area. If the high temperature heat source is used, I will decide the same value both the bore of the displacer piston and the bore of the power piston. When Vd and the bore is decided, the stroke is able to be calculated easily. The distance between the hot space and the cold space is important. When the high temperature heat sourceis used, the distance must be as long as possible in order to keep up the temperature difference. In this time, a long displacer piston is demanded (not the long stroke).


Q5: Why do you choice two piston type Stirling engine?

A5: Most of my engines are adopted two piston type Stirling engines (not displacer type). The two piston type engine can have a higher compression ratio (Vmax/Vmin) than the displacer type engine. I keep a compression ratio as high as possible. I desided that the compression ratio was setting about 2 for my model boat engines. I seem that it is difficult building a two piston type Stirling engine with metal pistons. Because a heat expansion of metal is big. The piston size is changed by heating. It increase a gas leakage or a mechanical loss.


Q4: Why do you use medical syringes for pistons and cylinders of most of your model engines?

A4: It is important that a leakage of a working gas decrease for model Stirling engines. When there is a lot of leakage, the model Stirling engine cannot operate or the engine needs a lot of fuel and high temperature for its operation. Most of my model Stirling engines are used medical syringes made of glass as pistons and cylinders. The medical syringe has few leakage with a few mechanical loss. And a heat expansion of glass is very smaller than that of metal. As the result, when I can use the medical syringes I can build a high speed model Stirling engine easily without my deep considerations. But the medical syringe is very fragile!


Q3: Can you please send the formula for Stirling engines?

A3: I have used calculation results of Beale Number when I design my model Stirling engines. I know that there are some high grade simulation of Stirling engines, for examples, isothermal model, adiabatic model and etc. Beale Number is the most simple model in Stirling calculation as I know. More information of Beale Number is here.


Q2: Can Stirling engines apply power source for small vehicles like motorcycles?

A2: I feel it is very difficult in the present situation. The Stirling engine is heavier than an internal combustion engine generally. I think that the Stirling engine does not suit such application.


Q1: What are Stirling engines better and worse than internal combustion engines?

A1: I think that the better points of the Stirling engines are a clean exhaust gas and a low noise. Of course it is important that the Stirling engines can use clean heat source like a solar energy and a hot spring heat. The worse points are heavy weights and high costs.


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Koichi Hirata

e-mail: khirata@gem.bekkoame.ne.jp (Home)
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