THE PULSE JET ENGINE
A pulse jet is similar to a ramjet, except that a series of spring-loaded shutter-type valves is located ahead of the combustion section. In a pulse jet, combustion is intermittent or pulsing rather than continuous. Air is admitted through the valves, and combustion is initiated, which increases the pressure, closing the valves to prevent back-flow through the inlet. The hot gases are expelled through the rear nozzle, producing thrust and lowering the pressure to the point that the valves may open and admit fresh air. Then the cycle is repeated. The most widely known pulse jet was the German V-1 missile, or buzz bomb, used near the end of World War II, which fired at a rate of about 40 cycles per sec. The pulsing effect can also be achieved in a valve-less engine, or wave engine, in which the cycling depends on pressure waves traveling back and forth through a properly scaled engine. A pulse-jet engine delivers thrust at zero speed and can be started from rest, but the maximum possible flight speeds are below 960 km/h (600 mph). Poor efficiency, severe vibration, and high noise limited its use to low-cost, pilot-less vehicles. Pulse-jets use the forward speed of the engine and the inlet shape to compress the incoming air, then shutters at the inlet close while fuel is ignited in the combustion chamber and the pressure of the expanding gasses force the jet forward. The shutters then open and the process starts again at a high frequency. This results in the buzzing drone for which the experimental pulse-jet missile is named the "Buzz-Bomb". People have pointed out that pulse-jets can be cooled which would solve the heating problem of the ramjets. They could also, theoretically, generate "donut-on-a-rope" contrails due to the engine's operational design.
a) Theoretically the pulse jet engine has a higher fuel efficiency than a normal jet engine that keeps constant pressure. Intermittent rather than constant fuel combustion is another key factor in making the pulse-jet engine more fuel efficient. than ordinary
b) Engines can be produced in many sizes with many different thrust outputs ranging from a few pounds to thousands of pounds.
c) They have a very high thrust-to-weight ratio, which means a lighter engine producing more pounds of thrust than it's weight.
d) They are mechanically very simple and have very little moving parts.
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