Valveless Pulse Jet
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
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
This picture show the connection of the metal tube connected to the combustion chamber
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.