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So me and my group mates in university got a lockwood hiller valveless pulsejet manufactured, and there was one error in manufacture. We are having trouble with trying to start the engine as demonstrated in the attached link. Is there an error in the engine you can see? One manufacturing error we identified is that the exhaust cone is slightly at an angle and is not exactly parallel to the combustion chamber+intake which looks something like the attached. Could making it parallel solve it? Also, would putting the gas cylinder upside down solve it?

The exhaust pipe is not parallel to the intake section

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    $\begingroup$ I don't have experience with pulsejets, but yours has other obvious differences from easy-starting versions I've seen on YouTube. Differences that seem more likely to affect starting and running than the angle of the exhaust. $\endgroup$ – Zeiss Ikon Nov 11 at 18:58
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    $\begingroup$ so the major differences you may notice is that the angle of the exhaust pipe is incorrect, but that same exhaust pipe is also too long, compared to other pulse jets, is there anything else noticeable I might be missing? The combustion Chamber is slightly larger as well $\endgroup$ – Ali Al Kayyali Nov 11 at 21:03
  • $\begingroup$ What is the pipe that you're holding to the intake? In other videos people seem to use a leaf blower to generate the necessary air flow. $\endgroup$ – Robin Bennett Nov 12 at 9:05
  • $\begingroup$ I am using 50 psi unregulated pneumatic power. The uni leaf blowers are all broken. With regulated pneumatic power the engine is not getting into that intermittent popping phase, just black smoke from exhaust, so we switched to unregulated pneumatic power. One thing to keep in mind that our pulsejet is large compared to other designs on youtube, and specifically the combustion chamber is also large, which means that maybe I’ll need to use more fuel? $\endgroup$ – Ali Al Kayyali Nov 12 at 20:43
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The key to the operation of a valveless pulse jet is the oscillating shock wave created by repeated explosions in the combustion chamber. In this video they talk about using a spark plug to trigger these explosions initially, and once the engine is running the process is self sustaining.

Looking at your video I don't see any connections to the engine except the fuel pipe, and you seem to be attempting to start the engine by pushing some burning material into the combustion chamber. This will not create an explosion, so the shock wave that keeps the engine running won't be created either.

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  • $\begingroup$ From my video watching, well made and tuned Lockwood-Hiller jets can usually be started (at least on propane) by a flame at the short end of the pipe, which propagates into the combustion chamber. $\endgroup$ – Zeiss Ikon Nov 12 at 12:04
  • $\begingroup$ I’m using this ignited cloth because it seemed to work with some other material here: youtu.be/qwuDkOB9Jik Also, colin furze (some youtuber) made a lockwood hiller pulsejet and one of the ways he started the engine was simply by igniting the intake with a torch, given that the gas is flowing out of the intake, which he recommends that the gas is flowing out of the intake initially, not the exhaust. $\endgroup$ – Ali Al Kayyali Nov 12 at 20:57
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To my eye, comparing with memory of many YouTube videos, the conical ends of the combustion chamber are too short and the bends in the exhaust pipe are both too small radius and the pipe is slightly flattened at those bends.

The angle of the exhaust pipe shouldn't matter -- I've seen these build completely straight and gotten to run -- but the sharp bends will produce out of phase shock wave reflections, and the too-short ends on the combustion chamber may also have a negative effect on the resulting gas compression.

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  • $\begingroup$ oh okay - your issue is with the tangents on the exhaust cone. This cone actually should have been rolled, but the fabricator had problems rolling it and their only solution was to create it out of tangents. I kid you not, I looked all over the country for a fabricator who can make the engine, and they were the only ones who can make it, let alone a reasonable price. The problem is our university is underequipped, and we simply do not have the time to buy the tools required and try to learn it. We do not have any rolling machines, welding equipment or laser cutters. $\endgroup$ – Ali Al Kayyali Nov 12 at 20:54
  • $\begingroup$ No, the tangents on the exhaust cone shouldn't matter. I was referring to the right angle and near right angle bends in the pipe between the combustion chamber and the exhaust cone -- these look, to my eye, too sharp (bend radius too small) and appear to have some pipe flattening. $\endgroup$ – Zeiss Ikon Nov 13 at 12:09
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    $\begingroup$ Update: I inverted the cylinder and the engine buzzed and pulsed, but I stepped off too early cause the exhaust explosion was too loud and I wasn’t expecting; I got scared basically. I was expecting yet another failure lol. Anyway, we tried starting it after that $\endgroup$ – Ali Al Kayyali Nov 13 at 15:08
  • $\begingroup$ Liquid propane delivers a lot more actual fuel than gas from the top of the tank. You may also find it helps to use a water bath (not too warm, please) to keep the tank from chilling as you draw the propane from it. $\endgroup$ – Zeiss Ikon Nov 13 at 15:14
  • $\begingroup$ oh so after that we tried to start it and it wont start and just blew a flame of wasted gas, as we checked the bottom of the combustion chamber it was freezing like you are saying. Is that a reason why it won't start anymore? When does that freezing happen, after engine is stopped? Or when it is running? $\endgroup$ – Ali Al Kayyali Nov 13 at 17:37
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This "university" project may have made an old mistake of scaling up before the design parameters were properly set.

A pulse jet, theoretically, is a truly amazing engine that uses an invisible piston to compress the next batch of air and fuel, a resonant shock wave. A properly shaped "tuned pipe" must be made or it simply will not run effectively.

So you may wish to start with a smaller, more reliable r/c model pulse jet as a demonstrator, rather than trying to get that monster to run.

Once experience is gained, move on to scale, keeping in mind the risk factors.

Tuned pipes also have application in increasing the output of 2 cycle engines by reducing losses of fuel and air out the exhaust port as the cylinder recharges for the next power stroke.

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  • $\begingroup$ oh and i forgot to tell you as well.. the engine was also never meant to be that big, but the company also insisted on the larger size as it wasnt feasible for them to fabricate the small ones, they had some ready made larger sizes so we had to edit the design and readjust the parameters to whatever sizes they had of parts. $\endgroup$ – Ali Al Kayyali Nov 13 at 5:28
  • $\begingroup$ the design parameters we followed were the 1967 original patent of this engine, and the exhaust pipe was supposed to be by most 130cm long, but when we had issues in manufacturing we had to go bigger.. I’m serious manufacturing has been that much of an issue so far $\endgroup$ – Ali Al Kayyali Nov 13 at 5:30
  • $\begingroup$ @Ali Al Kayyali you all may learn much from the experience. $\endgroup$ – Robert DiGiovanni Nov 13 at 7:44
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Just to answer my own question and not waste anybody’s time, all I needed to do was to invert the cylinder to get Liquid Gas to flow out. It worked! Here:

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