Pulsejet Problems
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- Опубліковано 1 гру 2024
- This is a 12 lb valveless pulsejet, built from plans provided by Eric Beck. The engine was built almost exactly to spec per the plans, yet it still isn't running. Any advice would be appreciated.
15/01/16
OK - First use a Roscoe Injector (see Pulsejet.com ).First -I think the tail pipe could be too short.Intake over powering the tailpipe.Work on one thing at a time to reduce the variables.Flames are what I call "blossoming" on the end of the tail pipe.You got to get that flame to go down into the engine.Use a slightly larger pipe on the to go over the tail pipe to adjust the length by moving the larger pipe outwards.That 'woowoo' sound is the flame trying to go down the tailpipe( think Rijke tube).With these bigger sized pulse jets it could be just a few inches out.Once you get that sorted - next is the intake.Cut off the flare - and do the trombone pipe thing for the intake length.Be prepared to vary your fuel injector position. Once you get the intake length sorted then make another flared end for the intake.Also try various angles of blowing the air in - get a cheap 12v raft/air mattress inflator and put a metal pipe on the end to extend it(stops the end getting melted).try varying the air pressure as well.Each pulse jet is an individual beasty and has its own starting and running characteristics .
You guys are getting there - close but not quite there yet. Once everything is tuned you will be away and laughing.Start it up with the tailpipe DOWNWIND - stops flame outs causing burnt eyebrow syndrome.
Oh yeah almost forgot - wear hearing protection and eye protection.
Good luck in your exploration of the new meaning of the word "LOUD!"
+Jutte777 Thanks so much for the input man! This is useful info! I've never even heard the term rijke tube before and now I've found out we made one xD
We had the idea of making some more pipe sections and sliding them up and down the intake and exhaust, but haven't tested anything yet. How tightly do they have to seal? And I guess we'd have to grind the welds down?
After reviewing some footage I took of the engine, I'm almost entirely sure it's the intake. There's a lot of dents and dings in it, and I'm thinking perhaps the intake is creating a lot of resistance and preventing oscillation.
Hi again. The sliding pipes don't have to be an exact seal- but the closer the better.I wouldn't worry too much about grinding the welds down - I have had a gap of almost 10mm and it still worked.That rumbling sound is good - shows that the engine wants to get going but not yet tuned in.The hardest I have tuned to get going were small straight pipe valveless pulse jets.It can get a little frustrating but then all of a sudden it will just take off be running. Good Luck.
+Jutte777 Thanks very much sir! Our science fair is tomorrow, and we managed to collect some data to present using jam jar jets. We are still going to try and get this thing working though, and use the trombone slides. When you say you had a gap of 10mm, do you mean between the inner and outer pipes (engine and slide), or do you mean the outer pipe is not welded into a complete tube (just rolled and left unwelded)?
Hi - for instance my tail pipe was 100mm diameter and I used a pipe that was 110mm in diameter. I was being lazy and just grabbed the nearest length of pipe for the slide instead of a pipe that was closer in size - so I was surprised that it actually worked.So after you have found the length that works - take note of the size then weld that size piece on the end of your tail pipe.With the really small Pulse jets where you can have trouble is the fact that the heated size may work - but the cold starting size is different - so the jet is hard to start but when it gets hot its a real screamer!
Good Luck and don't forget your hearing protectors !
Needs more air! if you reduce the fuel it will start to pop, thats getting close to the right air fuel ratio but by reducing fuel to achieve said ratio you dont produce the velocity required to create the vacuum needed to draw the flame back into the combustion chamber to continue the cycle. More air, it will run!
You need enough air to lean out the flames coming out the exhaust untill they turn blue and start to burn back into the tube. when it starts popping your in the zone. The fuel needs to "Bang" not burn.
and wear ear protection!
I recall that we tried various methods of forcing air into the engine without much success. At one point we tried a leaf blower but it blew the combustion right out.
Do you think we should try using sliding tubes to tune the intake/exhaust ratios like Jutte777 suggests?
@@markosfraser3030 yes ,adjust one parameter at a time. As was stated varying the air each attempt and if you can get hold of some sparklers to toss in the combustion chamber will make it much easier to get running.
I think the air is enough to start the engine
Get someone that is better at holding a blow dryer
+MysticalRooster xD Hopefully we can use the air compressor in the shop. That might get it started.
+MysticalRooster
Looking good so far. You need to give her more fuel, get it burning and then give it a good shot of air. Pulse jets love fuel! Give it as much fuel as you can burn with that setup and then try it. Just giving it gaseous propane should be enough to run this engine. Larger engines like mine use enough to where I have to feed it liquid propane to get a sufficient amount to the engine.
+MrBen527 Thank you very much sir! We find that if we give it too much propane, we flood the engine and we cant give it enough air to get it started. Do you mean we should get some yellow flames out the tailpipe and then blast it with air?
MArkos Frazzer
Yes, and as much as you can and then hit it with air. If you can't get a big burning plume initially, try pulling the fuel line back out of the intake more to draw in some more fresh air with the fuel flow.
+MrBen527 Thanks so much! We'll probably try testing this tomorrow! We're actually building this engine in order to test jet fuels for a science fair project, but if this engine fails we can make some jam-jar jets which will allow us to take accurate enough measurements to calculate the energy densities of the fuels.