Does anyone here know if there has been tried to make a Stirling engine without pistons? I have been thinking of a rotary engine which is based on the very same principals as the eccentric gear pump. On on the high pressure (hot) side, small air pockets between the gears expands, and the contraction will occour on the opposite side where the air is cooled. These forces will force the engine to rotate fully around its own axis - no other movements than pure rotary. No moving pistons which limits the efficiency.
Here is a video which shows how these pumps work: http://www.youtube.com/watch?v=Oyo3FrPCq28 (http://www.youtube.com/watch?v=Oyo3FrPCq28)
What do you think?
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