Hugo Lindner
how it works

Only hot air ....

If you think I am trying to describe the function of hot air engines here you are mistaken. 

I do not regard it as efficient to copy whole paragraphs from books or even other websites, only to repeat what is described correctly and comprehensively there in the same way.
I recommend the website of Peter Fette to you; it is very informative, containig information from the description of phenomena to the basic thermodynamic principles.

For those who prefer reading all this in a book, there is a new German edition of the authoritative work "Stirling-Maschinen Grundlagen Technik Anwendungen" by Martin Werdich and Kuno Kübler (ISBN 3-992 964-35-4), published by "ökobuch Verlag", 1999.  

You can also find an adequate historical survey of stirling engine development and many good books at this website: http://www.stirlingmotor.com/buecherd.htm

... but it works