If plethora of designs in search of perfection is an indicator of something of interest, then take a look at the many variations in valve gear design, particul

If plethora of designs in search of perfection is an indicator of something of interest, then take a look at the many variations in valve gear design, particularly for locomotives, which needed to operate reasonably efficiently over a wide range of speeds, gradients and loads. Even more so, consider the many attempts at making non-turbine rotary steam engines, wonderfully documented here: http://douglas-self.com/MUSEUM/POWER/rotaryengines/rotaryeng.htm http://douglas-self.com/MUSEUM/POWER/rotaryengines/rotaryeng... My personal favorite is the Tower spherical engine: http://douglas-self.com/MUSEUM/POWER/tower/tower.htm http://douglas-self.com/MUSEUM/POWER/tower/tower.htm Unlike most of the designs here, this one was built and even put to a little practical use.