Valveless Pulse Jet

Click here to see a short video of my valveless pulsejet engine.(857kb)

A valveless pulsejet is one of the simplest jet engine in the world. This jet was invented at the sixties, but the development stopped when the turbojet arrived. I've built my engine after the patent by Lockwood/Hiller (US patent no: 3.462.955). The engine can be built in many different sizes, as long as the relationships between the different openings are kept. This engine has no moving parts which means no wear, this is surely a benefit. It's also possible to run this jet with almost any oilproduct as long as it's valorized before it's entering the engine (I use a mixture of diesel and gasoline 50/50). The engine is started on gas (easiest). Construction is simple and relatively cheep to build. This is some sort of a pulse jet, and a series of explosions is what which make thrust. I don't know how many explosions per second, but I guess about 30 to 50. These series of explosions create an incredible loud and vibrating sound (30Hz to 50Hz). Pore neighbors....
Hope to measure the frequency some time.


The engine is started and powdered by propane feed into the
combustion chamber through this metal tube. At the end of the tube,
it's possible to insert a jet which may atomize liquid fuel.
When propane is used, I use no such jet, then propane flow through
a 4mm hole (M4). The metal tube is connected to the combustion
chamber by a M10 fitting. I've got three different connection
possibilities on the combustion chamber. One is meant to propane,
and the two other is meant to Diesel/gasoline injection.
This works great.

During starts, propane is feed into the combustion chamber and
ignited by a single spark from the spark plug. The explosion created,
make an overpressure which throw out hot air at both ends of the jet
at the speed of sound. While this air is exiting the combustion
chamber, a vacuum is created inside the engine. This vacuum force
the flame which is about to exit the exhaust pipe to return into the combustion chamber. Meanwhile fresh air has been sucked into the combustion chamber through the nozzle after the flame was thrown out. This cycle repeats over and over again until fuel is turned off. This is shown at the figure below.

From the patent, it's easy to construct a valveless pulsejet engine in every size. On my drawing below, you can see my engine based at the patent. It's a bit different than the patent (exhaust pipe), but it's just to make it easier to build. My engine is working very well, though I've not have made any thrust measurements yet. I've planned to make some augmenters, which is supposed to amplify thrust, and place them on my engine. According to some, thrust is doubled by using augmenters. I don't know about this, but it's going to be interesting.
Here are some abbreviations:


Click on image for details.

 

 

 

 





Propane bottles are sold at almost every gas-station. I bought a 11Kg bottle (industrial fittings) and paid 925 NOK. Refill is about 330 NOK. The bottle must be capable of high flow rate to power the engine. I use no regulator, only a needlevalve (meant for oxygen) to control the flow. The propane is fed directly into the engine through the main valve at the top of the bottle, the needlevalve, a hose and metal tube connected to the combustion chamber. I use no checkvalve, which may prevent fire getting back into the bottle. NB! I have never emptied a bottle while engine running. Bottle pressure is about 6 bar dependent at the temperature. Propane only burns if 0.9% to 2% of the mixture is propane and then rest of the mixture is air, so chances to get a fire back into the bottle is very small. (If you have got any corrections or disagree, please let me know). On the pictures below, you can see my bottle and setup. The hose is 10mm inside. (The metal tube is shown at the top of the document)





This picture show the connection of the metal tube connected to the combustion chamber

 

The sparkplug is inserted in a socket which are milled and welded to the combustion chamber. Any sparkplug would do. I use a regular "NGK BP6E S" without resistant. An old coil, removed from a car, is just perfect to make a spark. I've built a electronic circuit to power the coil. Remember only one spark is needed to start the engine, and then you stop the coil.

 

 

I have not made a final teststand nor any augmenter to my engine.


The engine is made of 3mm thick 316 L stainless steel. I don't know how to calculate wall thickness, but 3mm is probably more than enough. I have been running this engine much hotter than seen on picture (below) without problems.