Stirling Design - How to predict rpm

[cornwallav8r]

I am patiently getting up to speed with the mountain of stirling information, and have a quick question....
I located a Stirling design simulator, which computes output watts among other things based on design parameters entered...
But one of the entry parameters is rpm, as if it should be known or predicted during design...is there a relationship predictor based on cylinder sizes and throws that I am unaware of?

Thanks

[Ian S C]

All I know is that for high revs, use a short stroke, this also gives lower torque, and for higher torque and lower revs a long stroke is used, I,m afraid that what revs I get from a motor is a bit of a raffle, there are a lot of things affecting the out put of a motor, the heating and cooling, and all points of friction. Even the weight of the moving parts (inertia). even getting the correct weight for the flywheel, too light and the revs will be high, but the power almost nil, too heavy and there is too much friction on the bearings, absorbing valuable power. Then there is the heating! Speed also depends on whether the motor is pressurised, on not, and what gas is used ie., air, helium, hydrogen, or something like argon, all these gasses have different viscocities.
You may like to look at one or two sites on google: Simple perfomance prediction for Stirling Engines by Hoich Hirata. Schmidt theory for Stirling Engines. Or look at folksemantic stirling engines, you may have to dig around in this site, but it may be well worth while. Ian S C

[Charles]

My take is that you can't predict the RPM

The smaller the engine, the faster it will run.
I was recently watching a 10 inch Hayward Tyler - approx 100rpm
by contrast a 3/8 inch beta can reach 3000rpm

Piston friction and side forces also soak up the energy of the hot gas

The top speed of free running is probably determined by the effort of pumpage
The effort of pumping gas around the engine rises as the third power of the speed of the gas movement?
As the rpm rise, the gas speed rises, crawling up an ever steeper third power curve, the engine energy is definitely going to hit a brick wall

Another factor is that as the rpm rise, the time of each cycle reduces - and the heat transfer gets less effective as there is less time.

I think diminishing heat transfer time and/or pumpage limit the rpm

[Ian S C]

Even with moderate pressurisation, a motor built with modern materials could out perform the Haywood Tylerit is rated at 1 hp, a similar power pressurised engine would be a fraction of the size, ie., a little larger than the Phillips Bungalo generator set. Ian S C

[Just Ron]

For about $12.00 you can get a New E655 Digital Laser Photo Tachometer Non Contact RPM Tach on Ebay. And that is with free shipping. That way no guess work on your part.
Hope that helps.

[Ian S C]

Ron, the tacho is OK once you'v built the motor, but Charles wants to know at the design stage. I would suggest that you take a guess at a reasonable figure that would be suitable for the motor that you are designing, and design the motor around that, and if you'r lucky it will be better. You then use Jon's tacho!
Ian S C

[ScottTurow]

It may be powered by a broad variety of energy sources whilst it produces easily controllable emissions if any at all.

[Ian S C]

Rizwan, have a look on the 200W Stirling Engine help wanted thread. Ian S C

[saboor]

Greetings,I,v built two of these motors, stove top fans. The first a Ringbom motor was far too noisy with the free running displacer, the second a GAMMA type is most successful, it uses the normal ratio of swept volumes, ie the swept volume of the displacer is 1,5 that of the power cylinder, giving the ratio of 1.5 :1, this is the same ratio used by Stirling in his engines, and is the ratio recomended by the modern designers for high temperature motors. Ian S C

[Aviator168]

The amount of lost caused between the piston and the cylinder is the same, regardless of RPM. So shorter stroke, higher RPM. The other consideration is aerodynamic pumping lost which is generally higher if RPM is higher. As for predicting the RPM of an engine. It can get very high when there is no load on it. The first thing to do in designing an engine is usually come up with an use of the engine and its power output; you then figure what the best RPM is for that application, and so on.