Gatling jet

Jets that defy normal classification

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krzys Mnich
Posts: 11
Joined: Tue Jul 22, 2008 7:46 pm

Gatling jet

Post by krzys Mnich » Thu Jan 13, 2011 9:10 am


this is an old, well-known idea of the wave rotor combustor, but I've never heard of anybody, who tested it as a standalone jet engine. When made in garage, it could look just like a Gatling gun.
Imagine a bundle of metal tubes, rotating between two plates. Each tube works as a closed combustion chamber, so you can expect a big pressure inside.
Then, the exhaust pot opens (1), and the gas leaves the chamber, producing thrust. The rarefaction wave travels along the tube. When it reaches the opposite end, the intake port opens (2). The wave reflects, and the fresh air mixed with fuel flows to the low-pressure zone behind the wave. When the wave reaches the rear end, the tube is closed again (3). The shockwave
goes back, while the air still flows into the chamber. The wave passes the border between the air and the exhaust gas (4), then travels to the front end. We can neglect the weak waves, reflected at the border, as it don't influence neither the total mass, nor the energy of the gas in the chamber. When the shockwave reaches the front end of the tube, the intake port is closed (5). Then all is ready to the next combustion.
There is a problem about the combustion, since you need rather small temperature growth, so you should use a small amount of fuel. The simple solution is to inject the fuel in non-uniform way, to produce the rich mixture zone at the side of the tube. Such a mixture can be ignited by a sparkplug.

However, the deflagration in a long tube (7) will last unnecesserily long. It would be better to ignite the fuel in the whole tube simultaneously. It seems to be possible to produce a long series of sparks - see the picture. There is a row of small metal
plates, insulated from the tube wall. They form a series of capacitors with spark gaps between them. When connected to the sufficiently high voltage, this should produce sparks along the whole tube, almost at once.
The whole process repeats in each tube, subsequently.
Of course, the rotor needs some power to rotate. The simplest way is to use a part of thrust force to propel the rotor by twisting the bundle of tubes. Note that the tubes remain straight.
I've made some calculations - at ideal conditions, no energy losses, etc. The results are realy interesting.

I considered an example engine, made of 20 tubes 50cm long, 3cm diameter. The diameter of the engine will be 25cm. The temperature growth during the combustion is 150oC. In the pictures, the wave velocities correspond to the calculated ones - for about 1/2500s between the snapshots. The maximum pressure in the chamber is about 3bars, while the inertial compression of the air reaches 1.8bar. Max. temperature inside is about 300oC.
The rotation speed of the rotor - 10000rpm
The static thrust - 50kgs
The fuel consumption - 30litres of gasoline per hour
Pretty good, I guess.

The performance at speed is also interesting.
At 100m/s the thrust is 40kgs, while the fuel consumption remains the same.
At 200m/s the thrust grows to 43kgs, and the fuel consumption is 35lph

A have no idea, how much will it loss due to all the energy losses, leaks, viscosity, finite opening times, etc. but I guess it's worth testing.

Would anyone like to?...



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