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Hi, Futterama. I'm glad to hear your success!
The result that the pipe without inner spirals got the loudest sounds was interesting for me because I only tested the pipes with diameter more than 30 mm, and every test, I got the louder sound in case with inner spirals. I think that in the tube with small diameter, the spiral cause large flow loss than turbulent burning promotion effect.
For the downsizing of the length of small diameter D-cannon, the improving of initiator will be effective. I found the patent about the detonation engine by GE, and it was about the design of initiator.
The idea is very simple. Just connect the additional chamber with the diameter which is larger than the main tube. By adding this initiation chamber, we can obtain higher inlet flame speed and large flame sheet to main tube diameter.
This is the previous initiator unit for my D-Cannon. I Just connected gas torch to main tube.
The result was commonplace.
This is the improved one based on GE's patent.
In this video, the main tube was removed from initiator unit and this fire was made by just initiator unit. The result was really impressive.
So, by adding this kinds of initiator chamber for your D-cannon, you will be able to improve the performance with no change of diameter.
[Patent of GE about PDE]
http://www.ekouhou.net/%E3%83%87%E3%83% ... awing_area
Thanks for sharing, this is really helpful for my project!
I cannot read japanese, so can you try to explain how that patent works? Is it just a bigger diameter tube at the ignition place (drawing 1), or does it need to be a bit away from where the ignition takes place (drawing 2)? Also, did you put the spiral in the smaller part of the tube, the one that is closest to the gas burner (drawing 2)?
The images in the patent is a bit hard to understand without the text. Does the initiator internals look like drawing A or B?
Another question comes to mind. The shchelkin spiral you use, is that the same outer diameter as the tube inner diameter, or is there/should there be a gap between the spiral and the tube?
I think that we can get good improvement in all cases(1,2,A,B), however, I can't conclude which one is the best in practice. Just trying is the best way.
In my case, I connected the T-tube to gas-torch. By bending gas flow direction and impinge on the pipe wall, well filling of fuel into the whole area of chamber is achieved. In addition, I fixed the spiral into the chamber to promote the turbulent burning. Compared with the chamber without additional spiral, I got the more intense burning with spiral.
With regard to the shchelkin spiral, The outer diameter of spiral is equal to the pipe's inner diameter.
I made a video, showing the 2 meter tube with half a meter spiral inside. As you can hear, the first blast was bigger, so this is not a very reliable setup.
Next, I attached a simple initiator bottle between the tube and the gas burner, and holy crap, this made a huge difference! Unfortunately, the soft plastic bottle broke (not exploded, just cracked) before I could make any video with it, and also before I got around to finding my sound meter. But I did break a LEGO cardboard box with the blast pressure from the tube, this is awesome stuff!
I will make a new initiator bottle, and experiment a little with different tube lengths and bottle configurations, 2 meter is too much to bring along on the RC plane. The black and blue tubes are 20-21mm ID.
I also know of another kind of tube that might be useful, I have 2 sizes, 14mm ID and 11mm ID, but the pieces I have are too short, only 30-40cm long, so I'll have to get some more of this for testing. It is electrical tubing, for mounting inside a wall, where the wires go.
New initiator and more video. I had to change the butane tank in the burner right before recording these videos, I guess that is the reason for the blobby sound the burner makes, it didn't sound quite like that, with the old tank.
Anyway, still pretty awesome sound when it works. I'm not using any spiral in the initiator or the tube in those videos.
Your results is really awesome!!!
I haven't think that we can create intense jet in case small diameter tube like this.
I'll try small pipe as you did.
The tube is too small for real detonation as this requires a diameter of more than 51mm for the detonation cell to be formed using propane, according to the paper you posted a link to earlier.
But I guess anything above 340m/s would create intense sound and shockwave regardless of tube diameter.
Next step for me is more testing with different tube length, initiator size, with and without promoter spiral and so on. I need to find the smallest possible configuration so it can fit the RC plane.
Also, I need to get a gas/air mixer with higher flow so repetitive ignition can happen faster for a gun-like sound. I was thinking of building my own from lightweight materials like aluminium, I have seen a few videos on youtube about building a bigger propane burner. But I haven't found any information on how those burners achieve stoichiometry. I would suppose it is the ratio between the gas jet hole and the air intake holes, but I cannot confirm this theory on my own burner. I tried blocking some of its holes and the flame did change but not as much as expected. Any hints?
Re: Noise cannon for RC planes
I've been messing around with those Venturi nozzles for hybrid fueling, and I think I've got an idea to at least help your rate of fire issue a little bit. If recommend finding or making a very high flow Venturi nozzle and suitably sized "initiator tube" with a constant spark inside (like a taser circuit)
Your mixes will be a little inconsistent and probably lean most of the time, but I think it's the simplest way to get the highest rate of fire out of this sort of setup.
I love lamp
Lockednloaded, thanks for posting.
Can you tell more about those "high flow Venturi nozzle"? Maybe a link to something to help understand what you mean?
I will be controlling the spark timing using a microcontroller, but thanks for the suggestion.
My idea was basically making a bigger propane/butane burner kind of thing to mix the gas with air, and maybe add a one-way valve of some sort, but this would have to be something that is spring loaded to keep it open, and then the pressure from the gas burning in the initiator chamber should create the pressure to close it since there is not much pressure from the gas mixer stage. The valve would possibly help to get pressure in the initiator chamber faster, as I would suspect some of the pressure to "backfire" into the gas burner in my current simple setup since its basically an open end.
Last edited by Futterama on Wed Aug 10, 2016 4:16 am, edited 1 time in total.
Some technical progress: I used my 3D printer to print some cone shaped end pieces for attaching the burner and main tube to the initiator chamber. I re-touched the parts on the lathe where I needed more accurate dimensions. The pink PLA filament is all I have in stock right now, not very pretty or temperature resistant, but it works for prototyping
The main tube is now 130cm. With this working base design, I can now fine tune to smaller dimensions for better fitting in the RC plane.
So I have been experimenting some more. I have 2 other gas burners that uses those 330g/600ml propane/butane cans, same stuff used for handheld weed burners. I can't get any of them to work properly with my cannon rig. I mean, I don't get any real boom sound when using them, but when I switch to the Express 8800 burner (seen in previous posts) that uses pure butane, the intense sound is back.
I don't know if it's just that the Express burner is better quality and mixes air and gas in a more efficient way, or if it's the fuel, maybe the propane/butane mixes are of poor quality somehow. And I can't really switch to the propane/butane mix with the Express burner since it uses those butane gas cans that are punctured when you attach them to the burner, and the propane/butane mix cans are with a valve and threads.
The reason I'm eager to get it to work with the propane/butane cans is that it's much easier to make some lightweight stuff with that type of gas cans, I even found a lightweight 150ml can that will fit the RC plane perfectly. The Express burner needs a heavy cage around the gas can so it is kept pressed onto the seal around the puncture in the can. This is just too heavy for the RC plane.
I have been playing with the idea of buying a second Express burner, just to tear it apart and see how it is built. Then try to replicate it's design but make the gas attachment so that it can fit the propane/butane cans.
I also just finished building a big propane burner. Just as a fun small project on the side, and to learn a bit about the ventury burners. The middle piece is movable and is used to adjust the air intake. The brass tube can also be moved so the gas nozzle can be moved inside the tube, just to enable experimentation with different settings. A few minutes with this baby on, the temperature in the room rises quickly
Last edited by Futterama on Wed Aug 10, 2016 4:17 am, edited 1 time in total.
More update and some help needed!
I bought a new Express burner, the one I had already was item 8800, the new one is item 8900 and can burn upside down after only 15sec. So I took the old one apart and modified it to accept gas from the propane/butane mix cans. Success! The burner works just as fine on this gas as on the butane gas.
So I'm trying to figure out how this burner actually works and why this burner is better for the sound cannon setup than all the other burners I have tried. At least I know it's not the gas that makes a difference, so I need help on this
The construction seems to be very basic, there is a gas nozzle with air inlet holes around it. The gas sucks air into the mix using the venturi effect. The mix is forwarded into the dark steel tube, and before it exits, there are some small holes in the tube where a part of the mix escapes and flows through a very small circular gap. The outer brass tube is 16mm ID, and the ring that the mix flows around, is 15mm OD, so the gap is 0.5mm around the ring.
It seems like the steel tube is larger in diameter from the nozzle and to the small holes, maybe 6-7mm ID and then narrows down to 4.6mm ID at the final exit.
It is seen in the pictures that the gas that flows through the circular gap, is burning inside the outer brass tube. If the gas flow around that gap is blocked, the burner cannot hold the flame. Also, if that gap is blocked, the burner does not work for the sound cannon, no intense sound is produced, like with the other burners I have tried.
So for this burner, I think the circular gap and circular flame it produces, is used to keep the main flame alive. And also to light the flame with the piezo ignitor because the spark is in there with the circular gap. But why would this affect my sound cannon setup?
Could it have something to do with a larger backpressure on the venturi area when the small holes are blocked and this causes the mix ratio to change?
Maybe the ring-shaped gas flow promotes the mixing of gasses in my initiator chamber? But shouldn't the mix already be properly mixed since the gas burner can use the mix to hold a steady flame just fine?
The next step for me now, is to reproduce the Express burner design. I'll start out with a copy in the exact same dimensions and hopefully that will work. Next, I can experiment with different dimensions on the different parts to see what makes a difference. And maybe I'll try to double the dimensions for a bigger burner, and see if I can get that to work, and maybe this could give more flow in the sound cannon for faster shooting.
Enjoy the pictures and please leave a comment
I'm at the testing stage where I would like to have microcontroller support for the ignition so I can time the sparks accurately. I tried a simple breadboard setup but the electric noise from the high voltage module was so intense that it would reset the microcontroller. I even tried to run the HV module from a seperate supply and trigger it from the microcontroller through an optocoupler (which electrically isolates the module and microcontroller) but the microcontroller picked up the noise that was radiated from the HV wires. So since the basic idea is to put this system in a radiocontrolled plane, I can't have the module interfering with my other electronics, risking a crash.
So someone mentioned gasoline engine spark plugs, and I tried using a spark plug from the gas engine on my plane, but it seemed that the spark was too small or confined by the plug. Also the spark plug didn't protrude as far into the chamber as I'd like, so I'm having fun making my own spark plugs from 5mm bolts and solid core wire.
I'm planning to shield the wires but I'm not yet sure if I should just connect one of the HV wires to the shield and let the other wire run inside the shielding, like I have the bolt shielding the wire in the homemade spark plug.
Enjoy the pictures
All sparks generate a significant pulse of Rf. Indeed, one of the earliest radio transmitters was a simple spark gap.
Perhaps if the spark is inside a shielded container connected to the circuit ground and perhaps add bridging 1uF, 1nF and 1pF capacitors as filters? In other words, try to capture the spark's Rf before it can get to your other electronics.
jimmy101, thanks for the suggestions.
If I were to keep the spark inside a shielded container, I might as well make the initiator chamber out of steel, this has also crossed my mind. I think the open ends of the initiator chamber should then point away from any electronics if there is even any noise radiated through those small 20mm holes. There is something about hole size vs. wavelength but I'm not sure how that works.
Regarding circuit ground, the HV wires from the module probably carry AC, so is ground just one of the HV wires or are you referring to another ground?
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