I love to study uncommon engine designs and this video jumped out at me, I think you will like it.
Shout out to Minds Eye Design on youtube for this video.
Listed starting with number seven.
Sabre Engine - Speed up to mach25
Free Piston Engine - power extracted through exhaust gases.
The 5 Stroke engine - Say what??
The Duke Engine - Star Shaped Reciprocater
Nissan DIG-T R - 500Horse Power-->3 Cylinders...
Huttlin Kugelmotor - Power out of a ball ;)
Free Valve Engine - Electronic Timing to the next generation.
Hope you enjoyed this video!