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REVISED 10/02/02
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Ringbom Stirling engines differ from the usual kinematic Stirlings in that there is no physical linkage between the power piston and the displacer piston. Instead, the displacer rod is of a sufficiently large diameter that changes in pressure inside the engine cause the displacer to be moved between the top and bottom of the cylinder at the appropriate times. In his book "Ringbom Stirling Engines" Dr. Senft provides a mathematical analysis of the functioning of the Ringbom engine, and describes the "overdriven" mode of operation, in which stable running is assured by proper selection of engine dimensions.
My engine, pictured above was built to Dr. Senft's dimensions as outlined in an article in Model Engineer's Workshop", an English publication (September – November, 1982). While Dr. Senft's model was air cooled, I chose to modify the design to provide water cooling. The jacket around the displacer is filled with water before starting the engine. Denatured alcohol fuel is injected through the small hole in the base of the engine (visible at lower right in the photo). Two cc. will operate the engine for about 15 minutes
Some details about the engine
Power cylinder Bore, 1/2";, stroke 5/8";, displacement, approx. 2 cc.
Displacer diameter, .625"; stroke .625
Overall height, idle condition, 5"
DISASTER!
10/01/2002 Aquatap is no more! The aluminum free piston froze solid in the hot end over the summer. When I tried to free it, I managed to destroy both cylinder and piston. Later this year I plan to make a new cylinder/piston with stainless steel for the hot end and convert Aquatap to an air cooled engine. I will post photos when the work is complete.