The Germans used this type of engine during the W.W.II to power the well-known V-1 flying bomb. This power concept was eventually proven to be relatively inefficient, terribly noisy and also having a very short lifetime.
The valves on the V-1 engine lasted no longer than 30 minutes continuous use. The pulsejet was therefore abandoned as a full-size aircraft propulsion system. Nevertheless, it has been used on model aircraft by some enthusiasts until now.
A model pulsjet engine is basically made of a tube consisting of a head with a venturi shaped air-intake, a diffuser, a combustion chamber, reed valve plates, a spark plug and an exhaust.
In order to start the engine, a compressed air from an external pump or air bottle is fed to the angled pipe located near the diffuser while a pulsed high voltage supply is applied to the sparkplug. The air/fuel mixture is pushed through the valve into the combustion chamber and ignited, which causes a noisy explosion that closes the valve plates while the expanding gasses escape trough the exhaust. This produces a low pressure inside the combustion chamber that opens the valves and new air/fuel mixture enters the chamber again, which is ignited by the residual heat and gasses from the previous explosion.
The high temperature developed keeps the motor running without the spark plug and the compressed air, which are only needed at the start moment. Some types have no sparkplug attached. The initial ignition is then obtained by introducing external sparking wires through the exhaust. The pipe has an acoustic resonant frequency depending on its length, which must be close to the valves' working frequency in order to get a reliable operation.
Due to the extreme noise and the high temperature involved, this engine is absolutely not recommended for beginners and should not be used near residential areas.
