the Pulse Jet
is one of the simplest thrust producing combustion engines.
Its most famous use was in the German Argus engine which powered the second world war V1 flying bomb.
The engine consists of a carefully shaped combustion chamber with a one way air inlet valve and long tuned exhaust. Air and fuel is drawn through the inlet end of the engine by the exhaust gases departing throught he tail pipe. The resonant frequency of the tail pipe then produces a rearward pressure pulse which compresses the fuel/air mixture and closes the inlet valve. This mixture is then ignited by the residual heat remaining in the engine. This cycle repeats indefinitely as long as there is fuel available and nothing breaks.
The engines have no throttle control and their performance is fixed by the dimensions of the tuned exhaust and inlet valve geometry. in modern times, they are most widely used in model aircraft which can easily achieve speeds in excess of 350mph (although are, by all accounts, 'tricky' to fly).
I once borrowed a small (3 foot long) pulse jet which made so much noise that I lost the use of my hearing for a few hours after firing it up. While these engines are excellent fun, I prefer playing with gas turbines.