Flywheel Design

[Osama]

Hey!

I'm designing a Solar Powered Gamma Type Stirling engine with the following parameters: 70cc piston cylinder volume, 100cc displacer volume, Stroke of 39.5mm and crank radius of 19.8mm.

As far as I have searched online for Stirling Engine Designs, all the flywheel design has been a guess work. I may be wrong but found no such material for the flywheel design. Can anyone help me how to proceed with the flywheel design for the above stated Gamma Type Stirling Engine Parameters?

Thanks,
Osama

[Ian S C]

If you look in my gallery, you will find my large vertical BETA motor, it has a bore of 58 mm, and a power stroke of 323 mm, on that I'v used two flywheels 150 mm diameter, the thickness of the rim is 24 mm, and the rims are about 25 mm deep, so the the FWs are quite heavy, it will actually run quite well with one FW, it just looks better with two. As with a number of my motors, it will actually run without any FW at all. Ian S C

[stive951]

fullofhotair, short stroke, high revs, lower torque, long stroke, lower revs, higher torque, you pays yer money, and yer takes yer choice, the power total should in theory be the same. Ian S C

[theropod2]

fullofhotair, short stroke, high revs, lower torque, long stroke, lower revs, higher torque, you pays yer money, and yer takes yer choice, the power total should in theory be the same. Ian S C

I agree with the output power being the same.

Here's the thing, for me, that I think about a lot. With high RPM the output can be smoother, as a low RPM engine has a pulsating output with longer spacing between. This setts up a long wave sine wave, from what I've observed, in output. I have a small Kubota diesel single I use to charge batteries. It tops out at 1650 RPM and I drive a large frame semi alternator. At about 1200 RPM the engine can make ALMOST the same amount of power as it does at 1850, but the drive belt bounces in synchronicity with the power stroke really bad. I also have a small single Honda gas engine and it runs out best at 3400 RPM, and it will spin a belt to a similar alternator and load so much smoother it isn't funny. The Kubota sips fuel, and seems as though it's gonna run forever.

This could be the drive train, the belt, is reactive to these pulsations and variance in the linear speed of travel might have an influence I don't grasp. When I see films of old time steam engines and hit-n-miss engines running thrashers and such the wide flat belt they used is hopping up and down like mad, and those engines didn't run very fast either.

On my Kubota I softened this oscillation effect by repourposing a timing belt tensioner from a flat gear tooth belt drive overhead cam 2.3 L ford 4 cylinder. I use this little idler set to run very very lightly on the V belt's outside flat part. I've often thought of harvesting that tiny little wasted spinning somehow. This also seems to make my belts last a long long time. I usually change that out only every couple years.

The point being that the application should drive the design. If you can live with pulsating output a low RPM engine it might run longer between servicing, and McGyvering a work around like I did (maybe that idler could drive a Stirling cooling system) might make sense in some applications. Speed requires greater balance and machining attention than a lower RPM engine, however when any engine fails at peak output the results aren't usually good.

Sorry to ramble...

R

[Ian S C]

At our local museum we have a Ruston Hornsby 6HR oil engine of 28hp, these are a 1934 design of open crank horizontal engine the weighs about 5500lb, it has a 6ft fly wheel. These engines were available with two sizes of fly wheel, the larger was used for motors running a generator, because with the small FW, if the generator was connected to lights they flickered. Ian S C