I have been messing around with Pulse Jets for some time now and have made a few different types. The design below is a valveless type in that there are no moving parts whatsoever. This type of pulsejet is the easiest and quickest to make and it does not suffer from valve breakage problems that generally plague pulsejets.
Image links for this article : -
- Completed pulsejet connected up and ready to run.
- Layout drawing of the pulsejet giving component sizes.
- Detailed view of one end of the combustion chamber showing how it was made and welded.
- Closeup showing the gas inlet arrangement.
Links to the videos are at the bottom of this page.
The design below took me about 2 hours to make using bits of old pipe I had in my scrap pile. Follow the instructions and you can make one as well.
Before I start with the instructions - 3 things : -
- Pulse jets are very very loud - wear ear defenders and dont upset too many neighbours.
- The fuel for this engine is propane gas. When the engine is running the gas flow is quite high and if a flameout happens you get a big flame. You can see this in one of the videos! Be careful.
- If you chose to build one you assume full responsibility for your actions and by following these instructions, you agree that you alone are liable for any accident, injury or damage to property that may occur from the building or running of your pulsejet.
The layout view shows the general layout and tube sizes. The combustion chamber started as a 24cm length of 9cm x 9cm steel box section. The inlet end is a 10cm piece of 2,8cm ID steel tube. The exhaust end is a 70cm piece of 2,5cm ID steel tube. All the sizes are things from my scrap pile. This design works and will probably work with slightly different sized materials if you cannot find the exact bits.
Firstly, go and get your 3 pieces of steel section and cut them to the lengths given above.
Next, we will make the combustion chamber out of the 24cm piece of 9x9cm box section.
- Mark a line at 4.5cm from each end of the box section on all 4 faces at both ends.
- Mark the centreline of the box section on all 4 faces at both ends.
- Draw lines from the centreline mark at the end of the box section to the points where the lines (drawn in 2 above) meet the sides. Repeat for all 4 faces at both ends. The result should look something like this.
- Now cut along all the diagonal lines (shown in red on the picture above). You should be left with a 15cm long body with 4.5cm high triangles sticking out from each side of both ends.
- Put the box section in a vice with a set of pointy bits facing upwards.
- Using a large hammer, bend the triangles in evenly until they all meet at a one point. Turn the box section over in the vice and repeat on the other end.
- Place the 10cm steel tube over the point you just made and mark on all 4 sides where the tube meets the point. Cut off where you just marked to leave a square hole in the end of the combustion chamber.
- Using a half round file, file out the square hole until the tube will just fit.
- Turn the box section over in the vice and repeat 7 and 8 but with the 70cm steel tube.
- Weld each of the tubes in place and then weld the diagonal edges of the combustion at both ends. You should now have something that looks like this.
- Drill a hole to take a spark plug as shown on the layout drawing. The hole in my combustion chamber is around 14cm from where the inlet tube is welded onto the combustion chamber.
The spark plug screws into a nut that is welded to the combustion chamber. I managed to find a handful of nuts that fit sparkplugs when I was building my turboturbine. The nuts are possibly one of the harder things to find in the right size - mine came from a local garage out of a box of scrap suspension parts.
The only thing left to make is the gas injector. This is a piece of 6mm copper brake pipe. The pipe end is flattened with a hammer into a thin slitted flare and then the pipe is bent into a U shape at the end so that when the pipe is inserted into the lnlet pipe, the flare points away from the combustion chamber. Position the flare so it is roughly in line with where the inlet tube is welded to the combustion chamber. If you now bend the pipe back on itself along the outside of the inlet pipe, you can secure it to the pipe with a jubilee clip. This picture shows the view into the end of the inlet pipe. The flattened flared end is facing the camera roughly in the centre of the pipe.
To start the engine, you need an air supply (see the turbine pages for details), a spark supply (again, see turbine pages) and a gas supply.
- Turn on the sparks.
- Turn on the air.
- Whilst blowing air down the inlet, gently turn the gas pressure up. You will probably get a few backfires until you get the right combination of air flow and gas flow. Eventually, you will start to get a buzzing sound.
- Whilst maintaining the air flow, gently increase the gas pressure until the buzzing sound becomes stable.
- Slowly remove the air supply.
- If the pulsejet goes out, repeat from 3.
- When the engine is warm, remove the spark supply (or leave it on if you want) and turn up the gas. My engine will run from 2 psi up to 40 psi (maximum on guage)
- Remember to stay near to the gas valve in case it flames out.
Thats all there is to it.
Finally, for your amusement and education, there are 3 video clips below. There is a short edited video showing a brief run as well as 2 videos showing complete runs of the engine.
If you watch carefully, the cameraman jumps quite a bit when the jet backfires. The noise this thing makes completely overwhelms the microphone on the video camera but you can get an idea of the noise. The pulsejet is suspended about 6 inches of the floor in the videos mainly to stop it burning anything (it glows red hot). You can see the jet blast on the plants outside the workshop (we had to run indoors as it was raining quite hard).
- 33 second video showing an edited run and flameout (1.03 MB)
- 2 min 39 second video showing a full run (4.54MB) This shows the starting technique.
- 1 min 55 second video showing another ful run (5.09MB).
All the videos are Windows Media Player format (right click the link and select save target as to download)
If you have any question regarding the pulsejet or its construction, please email me.