double the pressure how much heat?

[Shanex-2]

I was reading in one of my stirling engine books ( stirling cycle engines by andy ross ) and if you used enough heat you could double the pressure. The question is how much heat is required to do so? Also does the same hold true for elivated pressures . would enough heat to make 14.7psi( atmospheric ) go to 29.4 do the same jump for an engine running at 300 psi .Would it go to 600 psi acting on the piston?

[Ian S C]

Shanex, first you are looking for the Kelvin scale of temperature, this gives absolute zero at minus 273 deg Celsius, then you want Boyle's law, part of which states that if you double the temperature (273 + ambiant temperature), in a confined space the pressure is doubled, so if the current temperature is 20 deg C, it is 293K double that it becomes 586K, there fore 14.7psi becomes 29.4psi. And yes if you go to to 300 psi, it will double to 600 psi, at these pressures the motor is a pressure vessel, and like a steam engine, or a compressor, should really be tested, even at the 200 psi that the Phillips motors use, thats quite a pressure. Ian S C

[Shanex-2]

ah ok . I didn't know if at higher pressures it would require less heat to double the pressure. I'm sure in real life there are variables that theory cant anticipate. It's a shame there isn't more power producing stirling engines out there kinda of like a Briggs & Stratton counterpart.

[Ian S C]

The Whispergen is I think pressurised to about 1200psi from what I can remember, I must find where they have moved to, thier old building is in the cordoned off area of Christchurch CBD. I know they got up and running fairly quickly after the February earthquake. Think the unit puts out 1Kw, early ones were .75 Kw.
You should find that you need to turn the heat up as the pressure increases, more air absorbs more heat, or to put it another way, if you want more power out, you,v got to put more in.
Sorry if you want Brigs sort of motor you'll have to build your own, many try, few succeed, but most satifying if you get someware with it. I see you'v read Andy Ross's book, so you have some idea what can be done, how about an Alpha motor with say 3" bore X 1.5" stroke, pressurised to 200psi. Ian S C

[Shanex-2]

yea I am glad whispergen is up and running again. I wish Andy was still selling his stirling engine kits. The model airplane motor he built was pretty cool you can see it in action on youtube by aross345 this is Andy Ross's channel. I also have an E-book that he wrote ( Makeing Stirling Engines ) and one of the engines he built had a bore to stroke ratio of 6 to 1. This does make sence concidering when you look at helicopters, there rotors move a lot of air at low velocity as opposed to the harrier jump jets moving small amouts of air at high velocity the harrier not being very efficent at hovering and require a lot of power to do so.

[Ian S C]

Shanex-2, a short stroke gives a low torque, high reving motor, where as a long stroke gives a low rev high torque one, the old type motors were the latter type, I think a high rev motor is the way to go, you can gear the out put to suit, and the motor is smoother in its out put. As the motor is geared down the torque goes up, of course its best for efficiency if you can drive what ever direct at crankshaft speed, for an example the motor in my pics with the hacksaw attached, think its a 4:1 reduction. Ian S C

[Shanex-2]

Nice . I also like the Ross linkage stirling you made.

[Ian S C]

Shanex-2, if you look at the Ross Yoke motor that is sitting on he bench for its first run , you can see the yoke, that open area there has a cover, yet to be fitted when I get round to designing a n effective low friction seal for the crankshaft, then I'll try to run it under pressure. The first seal I tryed had too much friction, and leaked too much. Ian S C

[Aviator168]

Isn't that why we don't see stirling engine in the market? The sealing is the problem. With the event of permanent magnet, magnetic coupling is the way to go. It is more expensive but no more than a electric motor.

[Shanex-2]

With the event of permanent magnet, magnetic coupling is the way to go. It is more expensive but no more than a electric motor.

true until you get to the bigger engines then they seem to favor double acting cylinders with roll sock seals.

[Aviator168]

Roll sock seals are great, but they still can wear out and still leak.

[Ian S C]

Aviator168, I think a properly designed and installed roll sock seal should last a good few thousand hours of running. I don't think the design of one of these engines is a home workshop project, but I could be wrong. The seal is made of Polyurethane, and highly flexable, I think that the oil spring on the side opposing the gas side would be the most difficult to design and build. Ian S C

[Aviator168]

No against roll sock seals. They are a pain to replace. They also have to be custom made to the stroke.

[Ian S C]

The only place I'v come across roll sock seals is the front disk brakes of a Holden station waggon(Aussie GM), there was'nt much problem there. The problem would be with the oil balance system. You would have to insure that the cooling was up to it, or you will soon cook the seal. If you can 1000deg C is around the temp you should be tring for at the hot end, and proberbly less than 40 deg C at the cold end. There is apparently a ceramic that can be applied to the stainless steel to prevent corrosion at high temperatures, and with care the fuel gas can be used to cool the cooling water,(you know how the gas bottle can get a bit of frost on it, the warm water helps prevent this) Ian S C

[Aviator168]

The only "roll sock seal" I saw was a rolling diaphragm. There is no oil seal on either side.