Failed Projects: Reflective Stirling Engine

This design failed admirably. I knew it would fail but the question was, "how badly." The answer was completely and utterly. At full sunlight the engine was spun over and not even a hint of pressure was observed acting upon the diaphragm piston.

Why did it fail? Knowing why this engine failed should help us to better understand how the Stirling principle works and doesn't work.


Hypothesis: How it was supposed to work: I had this idea that perhaps a semi-circular reflector could be used in place of the regenerator and displacer in an ordinary Stirling engine. The reflector would rotate to one side and block the heat, allowing the engine to cool and pull in the piston, which would rotate the reflector to the cold side. With the reflector covering the cold side, the engine should heat up, driving the piston outward and repeating the cycle.

Apparatus: A simple engine was created out of roll flashing, acrylic and wire. The wire was made into a cage and a sheet of tinfoil was attached to one side of the cage in a semi-circular arc. The cage was attached to a crank and a piston (diaphragm) was attached to the side of the engine with a breather hole to allow for expansion and contraction of a gas (air) to turn the reflector.

Results: Fail. Air does not heat and cool rapidly enough using purely radiant methods. In order to better heat the air, it needs to circulate. I had heard that "throughout history various attempts have been made to eliminate the displacer" and I was curious as to what those attempts were. Apparently, this is one of them.

For a successful engine, please check out my Stirling Engine Plans page.