pulse jet

The pulse jet engine is a cyclic reaction engine , independently patented in Germany and France in 1930 [ref. necessary] , and developed especially for the German V1 flying bomb during the Second World War .

Constitution

The model fitted to the V1 consisted of a long roll comprising a plurality of flaps in the front to completely close the air inlet, a combustion chamber equipped with injectors of fuel and candles and finally d a gas ejection nozzle.

Other models, such as the Escopette or the Hiller-Lockwood developed in France by Snecma , have no valves, but an intake tube often directed to the rear, because in practice it works also as a nozzle on half of the cycle and that, therefore, directed towards the front, it would brake the machine. This intake tube is shorter than the nozzle. When the gases escape at high speed, it causes a depression in the chamber and therefore a suction. This is weak on the side of the nozzle, long, because of the gases still coming out, while the side of the intake tube, the hot gas puff has moved away from the mouth and the air fresh can be introduced by the sides.

Operation

Animated diagram of the operation of a pulse jet
engine A) air intake & fuel injection
B) valves
C) combustion chamber
D) nozzle
E) gas ejection

The operating cycle (described in the gear reference ) is as follows:

Admission 1
The relative wind brings air into the combustion chamber through the open flaps.
Upstream of the chamber, fuel is sprayed into the air stream.
Combustion and relaxation 1
when the combustion chamber is cold , the candles cause the mixture to burn before it leaves the chamber.
When the combustion chamber is hot , the candles are no longer necessary: ​​the hot gases of the previous cycle are sufficient to ignite the fresh mixture and the combustion cycle is self-sustaining.
The pressure generated being greater than the pressure exerted by the outside air on the valves, they close. The valves are not strictly necessary because the simple fact that the internal pressure is stronger enough to prevent air from entering the front, a phenomenon exploited in a pulsoreactor without valve .
The combustion gases escape through the nozzle , with an increased speed (relative to their speed at the entrance) by their expansion, which generates the thrust.

When the pressure in the combustion chamber falls below the pressure exerted by the air at the inlet, the air can enter again to start a new cycle. If the valves exist, they open.

A cycle has a duration as short as the speed is high, often less than a tenth of a second. The Argus As 014 that powered the V1s had about 45 cycles per second, producing a 45 Hz sound frequency , in the audible range. It was even very noisy, giving the craft the nickname “buzz bomb” or “doodlebug” (chafer).

Advantages

  • It can, unlike the ramjet , operate at low speed;
  • It has the advantage of being of relatively simple and inexpensive construction.

Disadvantages

  • He is very noisy;
  • Its performance is mediocre;
  • It only works in all or nothing (no push control).

Use

Nowadays, we still find pulsoreactors on small radio – controlled leisure planes (see model ), because they are economic and simple to manufacture 2 .

Notes and references

  1. ↑ a and b Principle of operation of the Pulsoreactor , on pulsoreacteur.over-blog.com of November 19, 2005, accessed July 3, 2017 [ archive ]
  2.  RC Jet PulsoReactor with onboard camera , on monstertruck-team16.fr, accessed July 3, 2017 [ archive ]

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