metiz
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Posts: 297
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Post by metiz on Jun 13, 2011 17:04:23 GMT -5
Singing flame comes to mind, like a little experiment that you did at physics class, making this a Helmholtz resonator?
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wolfdragon
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Posts: 287
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Post by wolfdragon on Jun 13, 2011 17:27:46 GMT -5
honestly...
I had the fire extinguisher in one hand and the fuel valve in the other, and just cranked it wide open to see what would happen...
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Post by racket on Jun 13, 2011 18:01:42 GMT -5
Yeh , just combustion noises from the heat release , normally can't be heard over the compressor whine and jetnozzle roar , thats why flametubes fracture from the vibration and theres a screech liner in the afterburner .
You really need to have a thermocouple on the flametube outlet so you can adjust the fuel flow to obtain a "T I T " temperature of 1450 F to simulate actual running , you might find the flame colour will "improve" .
Cheers John
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wolfdragon
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Posts: 287
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Post by wolfdragon on Jun 13, 2011 18:49:27 GMT -5
a needle valve instead of a 1/4" ball valve will probably help too...
I need to make the transition tube from the back of that to my turbine inlet, will make a decently sweeping right angle turn, I plan on putting a P3 stagnation pressure pickup tube facing the combustor and then I will have a thermocouple probe at the turbine flange / transition plate, so the pressure and temperature will be sticking 90 degrees apart.
I also plan to grab stagnation pressure at P2 and P4 as well as those temps (and T1) just for grins and giggles
there is going to be quite a bit of 1/4" stainless tubing running around this thing when I am done... and that's just to give things room to cool off...
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Feathers
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Post by Feathers on Jun 15, 2011 19:56:16 GMT -5
The sintered stainless muffler is an incredible idea! I wish I had been the one to come up with that . One thing you might do is make a pass with your tig (if you have one) to the very "top" of that muffler to melt the sintered pellets flat, so you aren't injecting any propane directly down the flametube. Might shorten flamelength and lower temps. I'm using this idea for my pilot/preheat system! Thanks! Feathers
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Post by racket on Jun 16, 2011 4:31:38 GMT -5
Hi Feathers
Unless the sintered muffler produces "jets??" of propane that squirt out into the airflow to mix and burn , rather than just produce a "ball??" of propane that simply flows down the centre of the flametube , they're probably not a good injector .
Cheers John
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Feathers
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Post by Feathers on Jun 16, 2011 11:56:13 GMT -5
RACKET! WHY DO YOU KEEP MAKING SENSE?! I think I see what you mean. It's intended use is slowing down gasses, as opposed to spitting out jets of gas. An interesting idea though. I'm currently using a 1/8" hex plug with a small hole drilled in each "flat" of the plug. Feathers
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wolfdragon
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Joined: April 2011
Posts: 287
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Post by wolfdragon on Jun 16, 2011 15:21:18 GMT -5
Feathers,
I do have a TIG (Lincoln 200A inverter type) but since I figured it would "ball" more than "blow" I was rather hoping to not have to fuse the top of the muffler.
And, given the porosity and inherent oil content, there's no way I could pull a skin on top without just blowing through while just making a horrendous mess with the oil burnoff.
That combustor assembly is 0.035" 304SS, that was a 25 amp arc max, I don't even want to know what the max power for granulated SS would be (guessing less than 10, which is hard to do on my machine)
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Post by racket on Jun 17, 2011 4:08:59 GMT -5
Hi Feathers
LOL, probably because I'm an old fart thats been around for a while ;-)
There are "tank cleaning balls" that I've looked at using, they're all too big unfortunately ,......... heh heh , I don't need big balls, only small ones
Cheers John
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wolfdragon
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Posts: 287
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Post by wolfdragon on Jun 18, 2011 13:13:17 GMT -5
Well I finally figured out what all is going on with my flametube
the sound: Using local atmosphere properties (those actually inside the flametube) the sound is exactly on resonance with the speed of sound (temperature dependent) as well as the length of the tube.
the fire: Playing with the fuel/air ratio much more precisely than with a ball valve, I was able to use a fresh propane bottle to get a much more stable high-flow burn (until that bottle got cold too... i need to refill the grill propane tank) when i finally saw what I had suspected.
One thing to note, the airflow in my combustor housing and therefore the flametube is VERY rotational, I will post pics of how I did it, but it's much more rotational than axial.
The sintered pneumatic muffler emits flow in a ball pattern, the local airflow induced by the primary hole flow a few inches upstream causes the propane to spread out and swirl on the face and walls of the flametube, the majority staying toward the corner between the face and wall. The fuel and minor air mix stays in the boundary layer on the wall until it hits the primary zone, and this is where I figured out what was happening by quickly changing my ratios and watching as far back into the tube as I could see. The primary zone jets of air kick the fuel rich mix into the center and back toward the face of the flametube since there is no air holes there and the natural flow produces much lower pressure back there. As the length of the flametube increases to the secondary zone, there is no fuel left on the walls of the flametube and that is where I can see the end of the bluing of the stainless flametube. From there of course the flame front retreats from the walls and by the time the tertiary zone rolls around, the fire is well away from the walls and the cooling air is doing what it is supposed to do.
The oscillating between howling and not howling also showed me something. There are two retreat points over the burn spectrum, when the mix is very lean there are licks of flam that just stream out, these retreat back in as the burn actually gets going and the local low at the face of the tube where the injector and spark plug are gets established. BUT and this is where the burn changes from roaring to howling, when the burn temperature gets into the 1000+ degrees F ranges, the orange flame retreats all the way back to the secondary zone where the only thing you see is orange with wisps of blue where it looks like the flame caught some turbulence and got away from the burn zone.
So I started playing with the fuel mix at large swings and while the face was propagating back to where the stable zones were, when the yellow flames got out the way, back at the very front of the tube was a nice even blue flame firmly anchored on the corner and spreading a swirl of flame right down the center.
Lucky for me, the design of the my flametube and housing has the other side of that corner being directly cooled by air from the compressor.
So if I blow this cheap eBay turbo, I'm fairly certain that I have a good combustor to use on another turbo of higher quality and price.
Going to resize pictures, hopefully I will have some posted soon.
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Feathers
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Post by Feathers on Jun 18, 2011 15:06:02 GMT -5
Racket,
I've seen those! The little spheres that are riddled with holes, unfortunately they are very expensive through mcmaster carr.
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wolfdragon
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Joined: April 2011
Posts: 287
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Post by wolfdragon on Jun 18, 2011 17:16:10 GMT -5
ok picture time All parts are 304 stainless I made the Combustor Housing Face Ring out of some 0.035" wall 2" Tube The Flametube started as 0.035" sheet and had a 1/8" plate added to the front for a welding platform as well as where to put the holes for mounting the Fuel Injection Carrier Plate Then I put the Face Ring on the Housing (also made from 0.035" sheet) and added a piece of 2" Tube for the air inlet. Note how the air injection is fully tangential to the Flametube axis. Then I welded the Flametube into position inside the Combustor Housing on the Face Ring and a 0.035" close out plate in the rear And to finish out how to get fuel in there for my firing tests, The Fuel Injector Carrier Plate, the spark plug will go in the larger hole and will stick out an additional 1/2" from the nut Low fuel flow swirl pattern check Burn pattern after the flame gets situated, you can see the blue flame in the back spiraling from the injector to the front corners of the Flametube. Had to get that shot between big swings in the needle valve settings or else the only thing you can see is the yellow flame front. You can also see how the burn is shaped by the secondary zone, all the fire is behind them with the flame firmly rooted on that back corner all the way around the flametube. I think the build mascot approves And two new videos
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Post by Johansson on Jun 19, 2011 1:33:01 GMT -5
That´s one spaced out combustor! Are you going to convert it to liquid fuel later or is it a propane only combustor? Looking very professional, no doubt it will work fine on propane. (some air higher up in the primary zone wouldn´t hurt though, should get the combustion started earlier)
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wolfdragon
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Posts: 287
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Post by wolfdragon on Jun 19, 2011 8:45:07 GMT -5
That is jetspecs for hole calc and the Rules of Thumb taken at face value. The primary spread is 25-33% flametube length.
It is going to be a liquid fuel combustor when its all done.
If I need to add some air at the top end, I will probably put a jet for it on the fuel injector plate, but as it is right now, the fire sits all the way back there from the low pressure zone created by the plate seal and the primary zone location. I don't get more than a lick of orange flame coming out of the flametube unless I invert the bottle with all my valves wide open, and then it just looks like a propane torch when you have too much fuel for making the nice blue conical flame.
It's a first crack at it, if I need to change it then I will probably make another as the only takeapart is that fuel injector plate, everything else has a 1/8"-3/16" bead of 308/316 stainless holding it together.
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Post by stoffe64 on Jun 19, 2011 16:26:12 GMT -5
hello wolfdragon! is the flametube welded together with the outer plenum as well? it appears as it is so,then im afraid that it will buckle when it gets heated up in a running engine, it must be allowed to expand.....you are a very handyman with that tig welder
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