Beta engine measurements

Discussion on Stirling or "hot air" engines (all types)
Post Reply
Posts: 1
Joined: Fri Nov 02, 2018 7:22 am

Beta engine measurements

Post by miniripan » Fri Nov 02, 2018 11:53 am

I am planning to build a beta engine. I have found these “rules” about the measurements that a Stirling engine should have.
  • i. length of displacer chamber L = 3 times its diameter.
  • ii. length of heater chamber = 2/3L.
  • iii. length of cooler = 1/3L.
  • iv. swept volume of displacer = 1.5 times swept volume of piston cylinder.
  • v. length of displacer = 2/3L and stroke = 1/3L.
The cylinder is going to be made from a test tube with an inner diameter of 18mm. The displacers diameter is going to be 16mm. If my calculations are right, the power piston should only move ≈2mm. Is this correct? I’m concerned that the short distance will make the engine very weak and might not be able to run. Also, what material do you recomend the power piston to be made out of due to the glass cylinder?

I also wonder how big the flywheel should be. Is it a specific mass or diameter it should have for best performance?

I’m very thankful for all answers I can get.


Ian S C
Posts: 2218
Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: Beta engine measurements

Post by Ian S C » Sat Nov 03, 2018 2:19 am

Jonathan, your power piston is going to be 18 mm in diameter, if for example you made the power stroke10 mm, then the displacer would have a stroke of 15 mm, just make the displacer stroke 1.5 x the power stroke. You either need two cranks at 90* on the crankshaft, or it can be done with a single crank and a bell crank.

This little motor is based on a design by Justen Jones and was published in Model Engineer in March 1997, there are two versions, GAMMA, and BETA, but they are virtually the same, it has a power stroke of 1/2" and bore of 5/8", the displacer is 5/8" bore and 3/4" stroke and the displacer is driven by a bell crank.

The motor is powerful enough to drive the generator and supply 3V to run the Transistor Radio. It is fired with a meths burner, and is (mainly) water cooled.

Ian S C

012 (640x480).jpg
012 (640x480).jpg (199.87 KiB) Viewed 1946 times

Post Reply