In 1906 the first pulsejet was patented and since then has provided entertainment as well as opportunity for innovation and improvement. How a pulsejet works is actually very simple. With a valveless design (which this is), fuel and air are directed into a combustion chamber. Once the fuel has ignited, flame exits the exhaust tube and essentially creates a vacuum in the combustion chamber which draws more fuel and fresh air in. The ignition source would then ignite the fresh fuel and air for continued combustion.

This instruction manual will provide details on constructing and running a pulsejet that runs on isopropyl alcohol from items that can mostly be found at Lowe’s if not just lying around the house.

Project Steps

Beginning with the conduit box, drill a hole in one side (without the punch holes) to match the larger pipe (which will be the exhaust tube) and a hole in one of the two nearest corners for the smaller pipe (which will be the inlet tube).

Once the holes have been drilled, take the scrap metal and liquid weld it to the openings on the conduit box.

After the liquid weld has dried, screw the inlet and exhaust tubes into the holes drilled for them. Use the liquid weld to secure them in place.

Inserting the glow plug into the pulsejet will be fairly simple. There are a number of small holes already made in the conduit box. Insert the glow plug into one of these below the inlet and exhaust tube. This will allow the fuel and air to mix directly over the glow plug.

To feed fuel into the combustion chamber, begin by feeding a length of copper tubing down the inlet tube, stopping before contact with the glow plug. After this has been done, make a bend that directs the rest of the copper tubing down to the exhaust tube. Next, wrap what remaining length there is around the exhaust tube.

Since the copper tubing available only came in two foot segments when this was initially being done, and more than two feet is needed, multiple tubes will be used. In order to use multiple tubes, they will be attached by a segment of plastic tubing.

After the copper tube has been twisted around the exhaust tube, make sure the end inside the combustion chamber lines up with the glow plug and the cover is ready to be put on the conduit box. Once the cover is on and the screws have been tightened, secure in place with the liquid weld.

Take the bottle of isopropyl alcohol and make two holes. One at the base of the bottle, and the other just below the neck of the bottle. In the hole at the base insert the plastic tubing and liquid weld or hot glue the tube in place. For the other hole, insert the pin for the bike pump and liquid weld in place.

Now is the time to add everything together. Insert the plastic tubing from the spray bottle around the copper tubing that has been wound around the tail pipe. Connect a glow plug starter to the glow plug. Fill the bottle with isopropyl alcohol and connect the bike pump to it

Set the engine up outside so that it is stable and will not tip over. Using a air compressor blow air down the tailpipe. This will create a high pressure inside of the combustion chamber. As this is happening, with a hot glow plug, pump a bit of isopropyl alcohol into the engine to start the combustion process.

If the fuel is properly ‘sprayed’ into the conduit box (which means you may need to create a nozzle) and the weather is warm enough (> 50 F) then you should have created combustion. Beware that the aftermath of a running engine could ignite excess fuel spillage.

To improve efficiency and help to start the engine we recommend you spend some time producing a sprayed effect. This is you find a way to atomize the fuel coming into the combustion chamber rather than just letting it flow in from the fuel tank. This project does not cover how to do that, but be creative and you will have fun figuring it out.