okay vlalveless pulse jets are VERY arguable if they are good or not. for the money, they are fine. it's liek comparing the performance of a penu cannon to a combust with the same chamber and barrel. the penu will come out victor, but overall a combust can be just as good and cost less.
this has to be the BEST jet engine forum around, it also describes how they all work with fairly good example picture. i must say some people on their are REALLY good lol.
http://www.pulse-jets.com/
here is a really good explanation to a simple pule jet.
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NOTE i copyed this off of the
http://www.pulse-jets.comand am not taking any credit for this work.
The picture shows one of the possible layouts of a valveless pulsejet engine. It has a chamber with two tubular ports of unequal length and diameter. One port, curved backwards, is the inlet pipe and the other (flared at the end) is the tail pipe. In some other valveless engines, it is the exhaust pipe that is bent into the U-shape, but the important thing is that both ports point in the same direction.
When the fuel-air mixture combusts in the chamber, the pressure inside rises very suddenly. To an observer it looks and sounds like an explosion. The rising pressure forces the hot gas to expand out of the chamber and pass through the two ports at high speed. As it leaves the engine, the hot gas exerts thrust.
As the gas expands, the pressure inside the chamber drops. Due to inertia, the expansion continues even after the pressure falls back to atmospheric. At the lowest point, there is partial vacuum in the chamber. At that point, the momentum of the expanding gas is spent and the expansion stops. The process reverses itself and fresh air starts rushing into the ends of the two ports to fill the vacuum.
At the intake side, it quickly passes through the short tube, enters the chamber and mixes with fuel. The tailpipe, however, is rather longer than the intake, so that it takes incoming air longer to reach the chamber that way. One of the prime reasons for the extra length is to have some hot exhaust gas remain inside the tailpipe at the moment the suction starts. This remaining hot gas will now be pushed back towards the chamber by the incoming fresh air. When it enters the chamber and mixes with the fuel/air mixture, the heat and the free radicals in the gas will cause ignition and the process will repeat itself.
It took me almost 250 words to describe it, but this cycle is actually very brief. In a small (flying model-sized) pulsejet, it happens 100 to 250 times a second. The cycle is not much different, really, from that in the conventional flap-valve pulsejet, like the Dynajet. There, the rising pressure makes the reed valves at the front of the chamber snap shut and there is only one way for the hot gas to go -- into the exhaust tube. In the J-shaped and U-shaped valveless engines, the hot gas spews out of two ports. It does not matter, because they both face in the same direction.
Some valveless engine designers have developed designs that are not bent backwards, but employ various tricks that work in a similar fashion to valves -- i.e. they allow fresh air to come in but prevent the hot gas from getting out through the intake. We shall describe some of those tricks at a later point.
