home /
projects /
cv /
This is a weblog of what happens when 2 people decide to burn their fingers on what is said to be the most simple jet engine concept ever invented: the pulsejet.
This page is chronologically ordered. So far we have built 2 pulsejets. The first one was merely a prototype. We worked on this thing the first six days.
After these experiments, we created a descent propane-powered pulsejet
Benjamin has been making some calculations on the size of the combustion chambre versus exhaust pipe length. I've welded these pieces together, but we don't have a working pulsejet ... yet !
We made some snapshots, I'll put them online when (read: if) I find them back, because I don't know where (again, read: if) I saved them.
Well, I haven't found the pictures from day 1 , but this day is pretty well covered with pictures.
We started to work at about 10am at Benjamin's place. At that time we already had created the exhaust pipe and the combustion chambre and the valve system.
We attached the spark plug , and assembled the whole construction. (Note the Harley Davidson spark plug - nothing can go wrong with this magic part)
Then the construction was made ready for a first testrun. We needed compressed air to start the engine - that's where the compressor comes in.
For safety purposes, it's always a good idea to have a fire extinguisher at hand, in case thing get out of hand ( not unlikely if you see the pictures above :-)
After trying to ignite the pulsejet for the first time, we managed to get it starting, but didn't manage to keep it running. Most probably due to the venturi pump not working properly.
We experimented with WD-40 oil, gasoline, gas and methanol. After our initial experiments, we disassembled the pulsejet to perform some forensic investigation
We decided to replace our malfunctioning venturi pump with a direct gas injection into the combustion chambre. However, time was not on our side. It started to get dark outside, and decided to continue some other time...
After our second day of hard labour, we decided to pick up our initial experiments again. We figured out that since our pulsejet was not running smoothly, we had to redesign our venturi pump and our valve system. If this won't work, we'll try the direct gas injection.
It was a sunny day - but it was terribly cold (4 degrees). Apparantly the digital camera we have was configured to record black and white pictures. These are not pictures of World War 2 :-)
We found a piece of 0.15 mm steel (0.007 inch) , and cut 6 valves out of it. We mounted these valves the other way around, which is much easier to create than a flower-shaped valve. It also allowed us to create a simple angle limiter with an old screw you see in the rightmost picture.
These changes were partly effective. We managed to start the engine, but dodn't manage to keep it running. There still isn't enough airflow to get our venturi pump working without extra pressure from the compressor.
As another inconvenience, Benjamin's girlfriend didn't quite like the idea of us risking our
lives builing a pulsejet on this Valentine's day, as you can see on this picture.
We are quite happy with the inverse reedvalve concept. Today, we lathed a valve retainer for these valves using an iron ring that fits on the combustion chambre pipe.
Furthermore, we added a gas injector directly in the combustion chambre, and will be working with propane gas from now on.
We assembled our pulsejet once again, and started experimenting with our new gas setup.
After a lot of puffing and stuttering, we found the right gas/air mixture to start our contraption
The inner hole of our valve retainer was too small, so we needed to feed the intake with compressed air during the pulsejet run. But at least we got it running, and knew what we were doing wrong.
Our first mission was accomplished: getting a pulsejet prototype to start & run
Our next step will involve creating a descent propane-powered pulsejet, based on our proceedings.
Today, we will be experimenting with making reed valves by electrochemical etching. We purchased stainless steel of .1 mm thick , ethched reedvalves out of it, and tried these valves on our pulsejet prototype. You'll see some pictures of the etching process, and the result of powering out pulsejet with them.
Part 1 : cutting , degreasing and painting the steel (watch out - cut metal is sharp as a razorblade)
Part 2 : etching the reedvalves : 6V works fine
Part 3 : trying out the reedvalves of our contraption
This set of reedvalves only lasted for 2 or 3 minutes. This was partly due to the fact that we used stainless steel instead of spring steel, and partly due to the fact that our valve retainer had become too small for this set of valves. They just broke off.
We obsoleted the old pulsejet, and started focusing on a brand new design, built with professional tools. We first created a CAD design of our innovative inverse reedvalves, and etched a set of valves.
Notice that I used a low-power 12V transformator to etch the steel. The etching took exactly 25 minutes to complete (.1 mm steel) and the edges are really smooth. A lot smoother than with the high-performance ( 7amps-12V ) battery-charger.
Next up was a trip to Benjamin's uncle Leo to (ab)use all his tools for our purposes. We created an inverse air-intake in 2 pieces, were we will clamp our reedvalves in between. This assembled piece will fit in the pulsejet's combustion pipe very tightly, and screwed with 4 bolts.
These last pictures give a pretty good idea how the pulsejet will be assembled.
Time to assemble our pulsejet, and give it a spin. It worked perfectly. It started using compressed air and propane - and kept running after switching off the spark plug and the forced air intake. Hence, we have sucessfully built a working pulsejet , using an alternative valve technique.
Below are some pictures of the assembly, the running pulsejet, and the forensic investigation of the valve retainer. Our valves , altough not made of spring steel, did their job wonderfully. And keeping the engine running for 3 minutes, the valves didn't show any signs of wear (no change in color , rips or visible deformation due to the hammering against the holes)
Step 1 : miscellaneous assembly tasks and mounting of the pulsejet
Step 2 : running the pulsejet ; notice the orange glow due to the extreme heat.
Step 3 : Forensic investigation of the valve retainer : looks good
After that, we decided to assemble it again with another set of reed valves. Due to heat deformation, one of the screws in our aluminium intake plate broke off, and it leaked trough the top-left side. The result was desastrous for the aluminium. The pulsejet worked, but we had to shut it off after only 30 seconds. Another forensic investigation shows that this kind of leakage is fatal to the aluminium and the valves. On the other hand it shows that our new concept works, and is quite powerful.
Here are the parameters of our pulsejet:
Tailpipe diameter : 30mm
Combustion chamber diameter : 72mm
Reedvalves : inverse design ; 12 leafs 13mm wide
Holes in our intake are 8mm wide - radially extended using a mill over +- 10mm
here if an image of our CAD design for our reed valves, so you can etch your own. Have fun!
Here are some pointers you might first read before starting your own pulsejet project:
