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A simple Stirling Engine

This engine was built as a Gamma configuration which meant it had separate power piston and displacer piston assemblies.
The power piston was made from 25mm diameter brass and it was machined to run in a cast iron cylinder.
The displacer piston assembly was all stainless steel to reduce heat transfer as much as possible.
This engine design used a 'V' configuration to separate the displacer piston and power piston by 90 degrees. The main benefit of this arrangement was that both pistons could share the same crank pin and still be the required 90 degrees out of phase. 

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The power piston used a conventional crank and con-rod arrangement to drive the flywheel.

However the displacer piston used a Scotch yoke to connect it to the crank. The Scotch yoke was used because it reduced the side loading on the displacer, helping it run concentrically in the displacer cylinder.

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Initially there were problems getting the engine to run. It required extreme heat at the hot cap and ice cubes on the cooling fins to run at all.

After some investigation it was found out that the displacer swept volume should be 1.5 times the power piston swept volume for best running performance. This design had a ratio of 1:1 and because the stroke of the displacer was fixed a new displacer assembly had to be made to correct the problem. 

Short movie of the Stirling engine running