This liquid piston engine is not the usual Stirling Cycle type. It appears to run from steam and has no displacer piston loop. When starting, It does not matter if the tube is completely filled with water or if there is an air bubble inside. After heating, a steam gap or combination steam - air gap forms as shown in the drawing.

Presently I can not say for sure if this is a Stirling engine, a steam engine or both.

This liquid piston engine is simply an inverted U shaped copper tube connected to a clear vinyl tube. The clear tube is away from the heat and allows observation of the liquid motion. The copper tube is 3/8 inch outside diameter and the clear vinyl tube is 3/8 inch inside diameter. The brass fittings on the end of the copper tube are simply a means of sealing the end shut. The other end of the vinyl tube is open.

The clear vinyl tube is much longer than necessary because I did not want to cut it.

It runs well whenever it is heated anywhere on the right side of the copper tube up to the top. With heat applied anywhere on the left side, the liquid piston behaves much differently with an asymmetrical motion that usually settles to no motion at a higher level.

The tape at the top of the copper tube covers a small 1/16 inch hole which facilitates the job of filling the tube with water. (less info)