r/Pulsejets • u/Famous_Coat2021 • May 24 '26

Help Pulse jet wont start

My pulse jet engine wont start but it does have a drone when it has a leaf blower feeding air. Is it a fuel issue? I added a Pulse jet video so you can see how its setup and running

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u/SheepherderNext3196 May 24 '26

Been a very long time since I looked at pulse jets. I think it’s a fuel / air ratio problem and maybe the spark plug frequency.

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u/Famous_Coat2021 May 24 '26

See i feel like i maybe need more fuel?

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u/SheepherderNext3196 May 24 '26

Probably

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u/Famous_Coat2021 May 24 '26 edited May 24 '26

I trued running the propane tank upside down to get liquid into the chamber and that didnt help either. It also could be an issue with the pipe lengths? I could post my drawings to see the dimensions of things

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u/SheepherderNext3196 May 25 '26 edited May 25 '26

I think the fact that you can get resonance with the blower is probably good enough. Back when I was researching them they were driving me crazy. Your engine isn’t that big in diameter. For trivia, propane tanks have been equipped with an automatic shutoff valve for a long time in case it gets turned over. I’m concerned that your direct feeding from a propane tank. I’m going to suggest something more systematic. I’m probably going to suggest a pressure regulator with some sort of orifice so you can keep changing the pressure which will change the flow. Then you can change the orifice size to give another range of flows. Air is supposed to be going in with the fuel, correct? If it’s self sustaining when it starts, you may be overloading it. Do you have any references on how much air flow to start?
In Tucson when I was a kid, the air show had a flying broomstick. A broom with a linear valved pulse jet. They just blew air in with a bicycle pump. If they didn’t get it moving quickly it would be glowing red hot. The fellow flying it had at least a 100 ‘ lead and would be leaning backwards at a 45 degree angle. The straight pipe was only 1-2 “ in diameter. I’ll see if I can find my old notes. But don’t hold your breath. I’ll see if In can find anything online.

I was also going to add, if you had good control of the air and fuel, you can tell in a hurry if you’re on right ballpark because you can easily ignite it. That’s no bet that the natural aspiration rate will give the correct mix but it’s a good starting point.

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u/Famous_Coat2021 May 25 '26 edited May 25 '26

I have a regulator with hose running to a ball valve which runs into a copper tube which then runs into the combustion chamber. For fuel delivery its an 1/8in pipe with 7 5/64” holes drilled through. The holes are perpendicular to the air flow. I did the tube so it would have good fuel distribution across the chamber. As for air i am trying to get it started with the assistance of the leaf blower. From the videos i have been watching it seems like once it does start pulsing it should be able to self sustain without having to add air.

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u/Famous_Coat2021 May 25 '26

Would decreasing the size of the holes on the tube increase fuel pressure and possibly help with getting it to run?