http://www.ohio.edu/mechanical/thermo/Intro/Chapt.1_6/Chapter3b.html
I think UMS technologies are selling a working tabletop model of stirling engines...
http://umstech.in/view_products.php?cat=Stirling%20Engines
http://www.rcindia.org/rc-outlets-and-resellers/ums-technologies-limited/
In the 70's the Wankel Rotary Engine was supposed to spell the reciprocating engine's doom. Mazda used it for one generation of cars
(http://cdn1.automotobounce.com/pics/49/0d/Mazda-rx-8-wankel_e6b8d.jpg)
Fascinating concept. Read more on wiki here
http://en.wikipedia.org/wiki/Wankel_engine (http://en.wikipedia.org/wiki/Wankel_engine)
(http://upload.wikimedia.org/wikipedia/commons/f/fc/Wankel_Cycle_anim_en.gif)