PULSE JET WITH “CYCLONIC VALVE” PROOF-OF-CONCEPT MODEL

by John Tindall

During research on a recent project I began to tinker with pulse jet engines. This type of jet engine uses valves that open and close to allow air to enter after each explosion. The Germans had a complex array of spring reed valves that are beyond the capability of most garage inventors to recreate. I came up with a novel design that is simple to make that creates a uniform cyclonic airflow within the combustion chamber. To test my design I made a clear acrylic model. I hoped that the model would hold together long enough for me to see the interior airflow.

PULSEJETS were used on the famous German V-1 “buzz bombs” during WW II. But as far as jets go, they were destined to lose out to the efficient, dependable, and powerful turbofan jets that power modern airliners, fighters, and even helicopters. Maybe that’s their charm. It could be the knowledge that you are part of a battle lost long ago and forgotten by mainstream developers that draws in so many amateur science buffs to these dead branches of the jet engine tree of development. Whatever the case, pulsejet engines fit the ideal model for development in anyone’s garage because of a winning combination of attributes.

They are not complex to build, you only need a knowledge of welding and some metal working. There is vast online support. If you actually get one to work it is inefficient, red hot and louder than a boat horn. It may explode like a cannon and take out a wall of your house!

It’s easy to see why pulsejets have endeared themselves to so many hobbyists.

PULSE JET VS. TURBOFAN JETS Turbofan jet engines use a series of turbines to pull air in, pressurize mix with fuel and create thrust. It is a continuous process with air flowing through the engine in a non-interrupted flow. The pulse jet engine by contrast creates thrust through a series of explosions that are tuned by the length and diameter of the engine.

TURBOFAN JET ENGINE

image courtesy of aerospaceweb.org

VALVES SHUT Exploding Gases

create pressure wave and thrust

VALVES OPEN air flows into combustion chamber.

CYCLONIC VALVE DESIGN

Most people settle on a “flower petal” design that allows air to enter around the edge of the combustion chamber. This creates a lot of turbulence and makes for inefficient fuel mixing and airflow.

The proof of concept model was constructed of clear acrylic plastic and aluminum valves arranged to direct the airflow in a clockwise direction.

My theory: by making the valves follow a radial design a smoother (cyclonic) airflow would be achieved.

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Clockwise: The valves create cyclonic action. It definitely works. The valve and combustion chamber are attached to exhaust/thrust tube. Zoz Brooks PhD witnesses the pulse jet in action. The thrust blew lab coats off of their hooks. It is clear why steel is the preferred material for pulse jet engines – after running successfully for 20 seconds the jet backfired and blew itself apart. The remains of the pulse jet proof of concept model. The model did last long enough to see the cyclonic airflow. A Success! Now it’s on to the steel version!

PULSE JET PROOF OF CONCEPT ASSEMBLY INSTRUCTIONS

Cut out aluminum valves 1 ¼” x 1 ½“. Mark a 6” circle on the ¼” x 12” x 18” acrylic sheet. Drill four 1” holes at 12, 3, 6, 9 o’clock position on the marked circle. Mark and drill holes for mounting valves as seen in picture.

Use undersized bit and tape holes and thread acrylic with #8 tap. This will allow the adjustment of the valves so that they will seat properly.

Use backing nuts to lock screw at proper adjustment.

Rig up propane tank to certified pressure hose. Attach ½ “ copper pipe to hose via pressure fittings.

Put ½ “ pipe (fuel injector) into hole drilled in center of circle.

Heat pipe with short burn of propane.

While hot form 6” pipe around 2” pipe. Add electrodes.

Glue in place.

Complete!

Keep in mind that this proof of concept model by design was only expected to last a few seconds. The goal was to see the internal air flow to see if a radial valve design would create a smoother airflow. And it did! Now, on to the steel version.