Senior Project- Designing and building pulsejet

[TomMooijman]

Hello!
First we will introduce ourselves, our names are Tom Mooijman and Hessel de Boer.
We live in the Netherlands and attend a secondary school of pre-university education.
We are now in our senior year so we have a project, we discussed some subjects with our teacher and we both really wanted to build a Pulsejet!
We are probably not the only ones here asking for advice for a school project, so if it bothers you, we appologize. We were not sure to post this in 'Please put your "I am new and need help" question here.' but decided to start a new topic, since we can use quit some help. We have been going trough this forum for a while now, and we found it extremely helpfull for our project, so we would like to thank all you for sharing all this awesome knowledge!

Our assignment or project is about designing and building a (valveless) pulsejet, we chose to build a valveless pulsejet to avoid problems with the valves, we are aware of the fact that a valveless pulsejet is still really difficult to build properly. We are planning on buildind a chinese style pulsejet.
Desinging and building is not enough for our project, so we also have to try different fuels, the teacher thought about cooling the engine, and we are going to try to propell a bike with the pulsejet(we know, we have to build it first..). The teacher also thought about simulating the pulsejet in a program, does anybody have experience with that? I've read about UFLOW1D, but couldn't figure it out so far.

We've been looking for calculations on valveless pulsejets, but didn't have much of succes. We've read about the thumb rule 1,2 lb/sqinch, but does anybody happen to know about some more detailed calculations? The PyroJoes Recipe for beginning has been extremely helpfull, our first design is based on that recipe. We've worked it out in Solidworks, we are looking for about 14-15 pounds of thrust, that's why our Caliber is 50mm (If you prefer imperial, let us know).
Later on we would like to add augmentors, to improve performance (it was also an assignment to see how we can improve performance). And we have some ideas on injecting water in the CC. We know that because we've added cones to the design, it should perform a bit better.

Here is the first design we've made. We would like to know what you guys think, and all ideas are welcome!
We are not sure about where exactly the intake pipe should enter the CC, and should it inject further into the CC to improve mix of air and fuel?

All dimensions are in mm, again, if you prefer inches, let us know!

O, btw, we are planning to use 1mm Stainless Steel, and we've got a MIG welder.

Thank you in advance for your time!!

Tom Mooijman and Hessel de Boer

[metiz]

Place the intake at the centre of the choke-cone and put a small convex on the combustion chamber like in the drawing. 15-20 pounds is doable with this engine. If you're going to cool it, you might as well use the cooling water you're going to haul around and inject it into the intake for a ~50% thrust boost.

If you want to return the favour: how do you make mitred joints in solidworks?

[TomMooijman]

Hello Metiz!

Thank you for the quick response, and all the efford!
Thanks a lot for the advice! Tomorrow I'll make the new design, according to your drawing.
I think it is a very good idea to use the cooling water to inject in the chambre, we thought about winding thin copper tubing around the CC (or the exhaust too) and insert the end of the tube into the CC, can we just stick it in the intake pipe?

Ofcourse I want to return the favour! It took me some time to figure it out, I found a video very helpful.
Here it is: http://www.youtube.com/watch?v=VU8EjtD6Tgk

But I also made a 'Tutorial' on how to make a mitred joint.
If you've got any questions, ask.

This is the part on making a mitred joint.

Here is the part on actually creating the sheetmetal part.

Tom

[TomMooijman]

Today I made the improved design on Solidworks.
It took longer than I hoped, I had some difficulties creating sheet metal parts of the mitred joint.

Here it is:

It's a bit messy, I know.
If there is anything wrong with the design, let us know.

We are planning on building the Pulse Jet out of cardboard first, to see how all the pieces fit (should be perfect..).
There is a metal workshop in our neighbourhood, and they have a computerized plasma cutter, so we figured they can cut it out perfectly.

Tom

[metiz]

Thanks for the info on the mitres!

The drawing looks good! Solidwork must've given you so much shit for over-defining your drawing
I use google sketchup for all my designs and cutouts. Made this in about 5 mins

*internal cone, so no correction for sheet metal thickness*

[TomMooijman]

hmm, I might have to reconsider on using Solidworks I see.. Solidworks did give me lots of shit indeed, not so much on over defining because I made de dimensions driven. But it did on pretty much everything else..
I'll give google sketchup a try! And I think we can start building soon!

[TomMooijman]

It's alive!
Sorry, we've not been keeping you up to date on this project.
In the Christmas break we've been very busy with this project, we got the templates cut out in a workshop nearby, they used a laser cutter!
The templates came out perfectly, we then bended most parts by hand using the hinote slip roll, pretty tough but worked like a charm! We were able to roll the larger diameter with a slip roll in a workshop. We welded everything with a mig welder using 0.8 mm stainless steel wire, we had quite some difficulties(as we were not very experienced with welding 1mm stainless steel) but we got every piece together.
The fuelling system was interesting to build.. we were not able to find 3mm copper tubing(we spend a whole day driving around trying to find it) so used some left over 6 mm tubing. And pinched it with pliers as we found on this forum. It appears to be very difficult to find a propane tank connector without a regulator here in Holland, and when we found it, the guy was not too happy to sell it without using some kind of a valve, he was afraid the flame could shoot back in the line and the tank would explode, does anybody know something about that? We used a regulator for a torch so we could easily control the gas flow.
When we thought we could finally fire up this 'beast', we could not get it started, it roared for 3-5 seconds and then the sparkler would be blown out or just stopped. We tried to start it at my friends house, he lives on a farm but we were told to stop because the horses almost jumped over their fence.. We went to a different location to experiment with the amount of fuel and air, but we were stopped again after 20 minutes by a farmer who said his cows were going crazy..
So it was back to the drawing board, we decided to build a proper ignition unit, so we could have a continues spark. We ended up using a car ignition coil. We asked a garage for a ignition coil, capacitor and a Bosch-style relay. He gave us a modern ignition coil(with a capacitor built in) and a normal relay. He said it was not possible to use any kind of relay to give an continues spark, I did not agree. I did some research on the ignition coil, it has 3 connectors(picture below), b+, hall input, b-.

The garage told me the hall input triggers a magnet which will close a circuit so it will spark, its like a relay. So I figured we could use a Bosch relay to trigger the unit very quickly. The rest was pretty straight forward, I drew a circuit for the relay and connected every part.

If somebody wants a detailed circuit of the whole thing, let us know.

We tried to weld up some leaks and installed the spark plug, it worked perfectly after it warmed up a little!!

We are planning on changing one of the clamps, it doesn't really clamp down on the pulse jet, it only holds it in place. It is way too big for the CC and probably not very good for when the CC expands due heat.

We have to finish the project on January 14th, so we don't have too much time to do some extras. But maybe we will do those later for ourselves!! We sure got the Pulse Jet Rush.

We would like to thank everybody on this forum for the information which was already on the forum and especially metiz who gave some great advise!
You will hear from us again.

Tom Mooijman

[metiz]

Good to see you got it running! Those farmers are annoying aren't they? I mean, it's only like 157dB

For your propane question: No, the tank won't explode, nor will the flame retreat down the hose. For propane to burn, you need a mixture of, I believe, between 96 and 98% air and 2-4% propane. The tank has 100% propane under a lot more pressure than the outside air. Even if the tank had a pressure of 1 bar (atmospheric) you would be just fine.

Welding 1mm stainless is a bitch. Don't try to make a continues weld or you'll likely blow holes in your material. I bead my welds together, takes a while but gets the job done. (see attachement)

To weld under the intake: first weld on the outside of the intake as fas as you can comfortably go, then turn your welder (I asume 230v?) all the way up to the highest power setting, but keep the wire speed the same. Now finish the weld on the inside. The high power, low wire setting will kind of fuse the inside together instead of adding a lot of material.

Do you have a video?

[Jutte]

..."he was afraid the flame could shoot back in the line and the tank would explode, does anybody know something about that."

Yes Metiz is correct on that account the tank won't explode - mainly due to the pressure difference etc.
Interestingly the only case that I know of a propane tank exploding was in actually in Holland years ago.
After they had sifted through the wreakage of the house - they had found that the guy had
some how tried to modify the regulator - after that things apparently went west after a big "BOOM!"
Somehow air got into the tank (even the investigators were trying to work that one out)!
I saw a picture of the house and it was pretty impressive.

However with the normal fueling as used for Pulse jets you have no worry.
Just make sure your tank is in good condition and up to spec - No rust ,dents , correct date etc, or leaking main valve
and your good to go ! It's good to have some sort of main valve that quickly shuts off the fuel as well.
I used to fill the tanks up as part of my job - and I have heard alsorts of
wonderful misinformation from Joe Public about Propane/LPG gas.
Even most of the so called professionals didn't know diddly squat
as well.

[ace_fedde]

In the past (in Holland) it was possible to buy butane in bottles/tanks. The problems was that if those tanks stood outside in a harsh winter, the butane wouldn't evaporate anymore and could in bad installations even suck air in the tank. That led to a few explosions. After that it was forbidden to sell pure butan for houshold use, always a mix with propane or pure propane.
So always check which gas you use if in a harsh winter your stove doesn't want to ignite.

Fedde