Doyle Rotary Engine
Complicated? A little, but in motion it makes a lot more sense. The barrel, pistons and piston bores all rotate together, but since the barrel and chamber are offset, the pistons make one stroke per revolution. Intake air passes through the stationary center, past apex seals swiped from the Mazda Renesis rotary engine and into the compression chamber. When that piston reaches the correct angle, it releases the compressed air into the combustion chamber where fuel is added and ignited. The hot gas then passes through to the other row of bores where it expands, driving the power pistons, and then is exhausted.
Claimed Benefits: Since there's only one combustion chamber, there's only one spark plug, one injector and a simple ignition system. It removes a drastic number of expensive components from the entire engine equation. The immediate concern is engine responsiveness considering the amount of mass being spun around, but according to the engine's inventor, Lonny Doyle, when fabricated from aluminum it has less rotating mass than a normal piston engine.
Status: Despite the fascinating design and complex geometries, this engine is a one-man show. Doyle is a machinist at a race shop and is working on this engine in his spare time, using his own funding. His next big hurdle is finishing the machining of the second-gen design and coming up with a direct-injection system. Current price quotes for the one-off system are in the stratosphere, so he's definitely looking for investors.