Don't forget the 2 stroke diesel! Probably the simplest internal combustion ever invented. Few moving parts and no ignition!

They were popular as marine and industrial engines. Plus they could run either forward or backwards, depending which way you cranked them! :)

I work on a two stroke engine. Just a couple of points about it. Positive air pressure required by two turbo blowers to give up to 2.4 bar scavenge receiver pressure, fed to the cylinders when the ports in the liner are uncovered by movement of the piston. Fuel injected by two fuel valves(injectors)
6 cylinder, reversible, MCR=90rpm, bore 700mm x stroke 2200mm!! 20000bhp.
It's noisy but very reliable. Not much use for aircraft though as it's about 10 metres high.