Calculation for Alpha stirling engine

[lpkvh11]

Hi! I want to build an alpha stirling engine (my first). I have decided the following characteristics. Please tell me if it will work. I will grateful if anyone can give me the equations to find out power for the particular dimensions; or atleast refer me some good books (PS: i'm not very good at math)...
-stroke 56mm
-bore 50mm
-displacer diameter is 45mm and length 50mm
-cast iron cylinders and MS pistons
-will be trying both atmospheric air and helium as working fluid (any inputs?)
-crankshaft will have phase angle of 80-85deg (heard 90deg not optimum)
-recommended thickness for engine block? will be trying for more power by having pressure of about 3atm. (any inputs?)
-also please recommend good lubrication.

I'm aiming for at least 100W useful brake power. Please advise... Thanks!

[Chriske]

Hi,

Seems to me you choose a rather large engine to start with.
Best is to contact Andy Ross, he's an Alpha engine expert.
As a matter of fact, I've just started a Alpha project myself (B-20) with lots of questions.(I'm novice to in Alpha engines)
Mr Ross has a few nice, powerfull and fast running engines.

Chris

[lpkvh11]

Thanks for the reply chris. To be honest even i'm a newbie although i have been obsessed with stirling engines for the past 2 years... I'll take your advice and contact Mr. Ross.

This is going to be my final year project in engineering. I want to make a useful engine and not just for marks. That is my motivation. I'll be trying to use a heat collector (similar to one used in solar water heater) to collect heat. A fluid will be used to transfer this heat to the engine. Planning to use some salts or oil to transfer heat. Any suggestions? Please let me know if you didn't understand my idea...

[Ian S C]

Ipkvh11, I would suggest thatwith the size motor you are proposing, you will need to run the motor with the hot end 700deg C+, and the more pressure, the more heat (not temperature, ie., a match can be as hot as a bon-fire, but the bon-fire may have thousands of times more heat.
Transfering heat by hot water would power a Low Temperature motor.
It's normal for the two pistons to have the same bore and stroke in an ALPHA motor, and rather than a displacer, there is a hot cylinder, and a cold cylinder both with fitting pistons. The bore and stroke can be varyied as long as the capacity remains similar, but having them equal makes materials easier, I made my Ross Yoke engine by boring the two cylinders as one, then parting them after I'd finished, both pistons lapped to fit down the full cylinder. Ian S C

[Chriske]

I made my Ross Yoke engine by boring the two cylinders as one, then parting them after I'd finished Ian S C

Something to remember...!


Chris

[Ian S C]

Personally, I would reduce the stroke to about half of that quoted. Ian S C

[lpkvh11]

Ipkvh11, I would suggest thatwith the size motor you are proposing, you will need to run the motor with the hot end 700deg C+, and the more pressure, the more heat (not temperature, ie., a match can be as hot as a bon-fire, but the bon-fire may have thousands of times more heat.
Transfering heat by hot water would power a Low Temperature motor.
It's normal for the two pistons to have the same bore and stroke in an ALPHA motor, and rather than a displacer, there is a hot cylinder, and a cold cylinder both with fitting pistons. The bore and stroke can be varyied as long as the capacity remains similar, but having them equal makes materials easier, I made my Ross Yoke engine by boring the two cylinders as one, then parting them after I'd finished, both pistons lapped to fit down the full cylinder. Ian S C

700deg C seems a lot ! I'll try for a less ambitious power for now.

[lpkvh11]

Personally, I would reduce the stroke to about half of that quoted. Ian S C

Will try to make some adjustments. I'm also looking to use the Ross Yoke mechanism. Runs smooth it would seem...

I have found a Final term project report of some people while browsing randomly for a long time. They got about 95W from their alpha with regenerator. But theirs is not Ross Yoke mechanism. Wonder if I'll get more power if scale up the engine a bit and use Ross yoke...

[Ian S C]

As you scale up, it gets more difficult to get the heat into, and out of the engine, the bigger engine needs to get quite complex in the heat exchanger department, I think it may often be best to use multi-cylinder engines, rather than one large cylinder, a small motor, say 50 mm bore 25 mm stroke might run up at about 2000rpm, where as a motor of 200 mm by 50 mm stroke would be pushing it to get to 500 rpm with out a load, and half that with a load. I find its better to gear down from a higher speed if need be that the other way, but which ever direction the gearing careful matching helps,ie., gear so the motor runs at optimum speed. Ian S C

[lpkvh11]

Did some extensive googling and you are right. I found Andy Ross's "Making a Stirling Engine" ebook and am very interested in the D-90 engine he built . It has a 57.9mm bore and 24.1mm stroke. It uses the ross yoke mechanism and so the the "crank throw dia" is 17mm. Please tell me what "crank throw dia" is.

Also the D-90 is an alpha type. The air from power piston seems to flow all around the displacer piston's cylinder through the regenerator and then through some dead space and then into the displacer's cylinder through annular fins at the very top. Am i right is assuming that the regen, cold side n hot side hug the displacer's cylinder from the outside? Will it be as effective if I use a separate regenerator from the power piston cylinder to the middle of the displacer piston cylinder? I hope you can understand what I'm trying to convey... Please let me know if you don't understand.