A pulse-jet is a type of air-breathing engine in which air is compressed by a series of spring-loaded, shutter-type valves
located ahead of the combustion section. As in a ramjet,
compression is achieved without the use of a compressor; however, whereas
combustion in the ramjet is continuous, in the pulse-jet it is intermittent.
Air is admitted through the valves, and combustion begins. This increases
the pressure and closes the valves, preventing backflow through the inlet.
As the gases expand through the rear nozzle to produce thrust, the pressure
in the combustion section drops to the point where the valves open again
to admit fresh air. The cycle is then repeated. The basic idea for the pulse-jet
came from Paul Schmidt, of Munich, at the start of World War I but its most
infamous manifestation was the German V-1 "buzz