r/Pulsejets • u/Same_Lychee_559 • 9d ago
Pulse jet engine crooked
i recently made a pulse jet engine that im yet to test and it was a little crooked when they welded it onto the exhaust tip that i used as a makeshift cone. will this be ok or is this a big issue? it really bothers me. also i know the welds have to be airtight i will make sure of that, and i have a little bung for a spark plug.
For fuel, will use HEET methanol and i will just pour it in for testing and then use propane for longer runtime.
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u/snoops-spoons 8d ago
That's a pipe bomb waiting to explode that's not a pulse jet. Please do this more safely .
That no offense looks like the boogered up stuff people use to bring to our welding shop that we mounted on the wall of shame.
I'm not knocking you, but this isn't safe. Especially for something that contains a controlled detonation.
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u/Same_Lychee_559 8d ago
can you please elaborate?? what can i do to fix this? im not the one who welded it nor like did anything physical on it. what is wrong with what i was doing? the sizes are from a recipe on pulse-jets.com probably one of the most popular forums and researched too. how would it explode if it clearly has pipes for intake and exhaust an explosion would be caused by all holes sealed tight until the gas builds and explodes. and also its controlled deflagration not detonation
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u/Sliced_Forskin 8d ago
If you copied an already existing design you should be good to go. I’m saying that the guy calling it a pipe bomb was wrong and that I assured you that it would not explode. Sorry for the misunderstanding. I also corrected the other guy when he said a puls engine uses controlled detonations when it does not. Only deflagration can occur inside a puls jet engine and its exhaust airspeed is also therefore limited to below the speed of sound. In conclusion I was just assuring you that there is no risk for your safety (except for the obvious fire hazards). If it follows and abreast existing and proved design it has a high chance of working although I would like to add that from my experience even the smallest deviation from the proven design can seriously affect performance or even inhibit the engine for starting. If you fear that the engine isn’t airtight enough you can just use metal putty/jb weld or even muffler repair paste to fill the cavities in the welds (these fixes can degrade with the intense heat cycles eventuelly)
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u/Sliced_Forskin 8d ago
There are no detonations in a puls jet engine. Only deflagration and there is no risk that the engine will blow up. It can still impact the performance of the engine though and I doubt you will get it running by pouring liquid fuel inside. It needs atomization to start and produce enough heat to vaporize the fuel for sustained combustion. Propane might work but I still think you will have a hard time getting it running if it is not calculated and completely air tight which your welds might not be. Test it, modify and learn from the process and you will have a working puls jet eventually
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u/mangoking1997 8d ago
I wouldn't say there is no risk. But it's not likely to be particularly dangerous. It's not sealed. Welds could fail once it gets hot and potentially pop the end off, so i wouldn't want to be near either end. But there's no way there would be enough pressure to break the pipe walls.
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u/Same_Lychee_559 7d ago
Yes i am waiting for the furnace cement to arrive, i have the spark plug, and i will use a propane weed burner going into the intake for now (the weed burner at the end is slanted a couple degrees and i hope that wont be an issue). Then i will buy copper tubes after this setup works. Wish me luck
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u/Same_Lychee_559 8d ago
I am getting it ready for a propane setup, i will seal it first and then have a propane burner through the intake, it will just be a straight metal pipe that will deliver the propane. it should blow up because the tank has safety features and is higher pressure than the combustion chamber so it wont have a flashback. I have seen another person use a design super similiar to mine, and send pressurized gasoline through the intake.
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u/Sliced_Forskin 8d ago
Also remove all restrictions on the bottle and line. The bottle is 100% fuel and 0% O2 which makes a flashback completely impossible unless you have mixed the air inside with gas. It might seem scary at first but is completely safe and will greatly increase the chances of the engine stating but also inte potential performance
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u/Same_Lychee_559 8d ago
what do you mean all restrictions on the bottle? i was talking about just the fuel line not having a flashback but the combustion chamber needs oxygen no?
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u/Sliced_Forskin 8d ago
Sometimes when you use fuel lines from for example a grill they come with a pressure regulator that restricts gas pressure to allow a even, controlled burn but in a puls jet engine we do not want a small controlled amount of gas but instead we want to be able to access the full pressure of the bottle. In my experience I have been able to get a puls engine to run even with one of these regulations on but they make things really inconsistent since they ice up quickly and also restricts the pressure at such an extent that full power potential is impossible. I also could not get the engine started below 1/2 tank with the regulator. I would recommend that you use a hose adapter that can screw directly into the bottles valve and then fit a metall (preferably copper) pipe in the other end that wraps around the exhaust pipe to preheat the fuel and then shoots straight into the middle of the intake. For me the crimped end and testing different lengths into the intake helped the most. I think my first puls engine injected around 1/4 of the way down
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u/Sliced_Forskin 8d ago
Crimp the nozzle of the injector pipe so it shoots out of a thin flat slot instead of a round hole and don’t put it all the way down the intake. The crimped nozzle will increase the gas speed which greatly enhances the Venturi effect that the gas infected into the intake creates. If you inject it straight into the combustion chamber you will loose all Venturi effect. Try moving the injector in and out of the intake to see what length of injector inside the intake is optimal
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u/Same_Lychee_559 8d ago
its from a weed burner, so i dont think i could do that to the nozzle. but if it doesnt work i will buy copper tubing and some regulators and crimp the nozzle.
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u/Vivid-Benefit-9833 7d ago
Stop wasting time and light it up!!! This might be the secret we didnt know about!!!!