Sunday, October 4, 2015

Working shuttle prototype!

Simplify, simplify...after about a year of prototyping, I finally sent out some feelers and did some networking with some other fire artists, to get some feedback on my designs.  I had a good conversation with DaveX from BMOrg, who made a couple of observations that stimulated a line of thought that I had been rolling around in my head for a while.  I hacked together a prototype out of 6" diameter HVAC conduit and off-the-shelf end-caps.  All the "machining" I had to do with it was to cut a 1" slot freehand with an angle grinder, and I cut some strips from the leftover which I screwed into it to form it back into a rounder shape:

I drilled some holes in the end caps for the rails, and used the end caps from the previous prototype to hold them in place.  Then I threaded the old shuttle onto it.  With just the slot in the top, the effect is nice, but the flame is very concentrated, and it definitely has the aesthetic of something mechanically moving the flame underneath:

BUT...(and this is where DaveX's suggestion comes in), I then fit some aluminum screen over the slot, and laid some steel wool over it to use as a diffuser.  The effect is a much more organic-looking flame:

I think this looks great, and it's incredibly easy to build.  The only welding and machining is of the shuttle.  I have some issues with the hose tracking to work out, and I need to motorize it.  But this is going to be the basic design I'm going to go with for the eventual build.  I may even extend these to 8 feet long, if I'm going to start with a pyramid instead of an icosahedron, just to make it more impressive in scale.

Tomorrow morning, I'm going to start a new venture, starting up a software company.  That may or may not work.  But it is going to take up a lot of my time and my vacation is officially going to be over.  I'm very satisfied that I have a working prototype, and even if my progress slows down, I know I can get this up and running eventually.  Onward, and upward.

Friday, October 2, 2015

Shuttle prototype v5.2: Getting Better All The Time

Spent some time testing the shuttle prototype with various air intake mechanisms, some of which produced better results than others, but none fantastic.  After the intake fan burnout I decided to go with MOAR AIR.

I had two main strategies: air mixing with the gas line, and forced air into the sheath.

My initial gas mixing strategy was to inline a vacuum ejector into the gas intake, but this had no discernable effect on the output flame color or constitution, so I got rid of that quickly; if there were significant enrichment of the flame with air, I would have seen a much bluer flame, due to more efficient burning of the propane.

To test a compressed air source, I tried to build a ghetto fabulous compressor by hooking a really cheap 12V tire compressor to an old propane tank that I had converted into an accumulator:
 This worked a bit, but it took about 30 minutes to pressurize the tank to 40 PSI, and after the third time, the poor little compressor blew a gasket.  So much for plan A.

Plan B was to rent a compressor:

I hooked this up with a T into the gas line, with a check valve at the gas line to make sure the air didn't flow back into the gas line.  The compressor went up to 120 PSI, but the regulator on it wouldn't go above 60 PSI.  This turned out to be plenty though, at least for my initial tests.  Simply mixing the gas with the air, even at 20 PSI, would blow out the flame.  The regulator didn't go much below 20 PSI, so I installed a 1/4" needle valve so I could make fine adjustments to the air flow.  I wasn't able to get any improvement over the usual observations: poor flame, mostly confined to the sheath and blowing out the ends.  This was at low gas and low air flow.  At higher air flow, the flame would blow out, and at higher gas and air flow, it was about the same.

If I removed the shuttle from the sheath and ran the gas at 30 PSI, it produced a great flame.  If I slowly introduced air, I could create a nice blue flame, clearly modulating the air/fuel ratio.  By adjusting it this way, out of the sheath, I was able to ensure that I was getting the right ratio.  But putting the shuttle back in situ, the results were very similar to before, little or no sustained flame.  This suggests to me that the primary issue may not be air mixing, but ineffective ventilation of the exhaust: as soon as the gas starts burning, exhaust builds up in the chamber and snuffs the flame.  I would still expect the gas to burn under these conditions if I'm supplying enough air.  But it's possible that the "correct" ratio that I see with the shuttle in the open air is a result of the introduced air + the atmospheric air, and that in a confined space, the lack of the latter is enough to kill it.  This would suggest that it IS possible to supply enough air with the fuel, possibly.

I next tried an air manifold that inserted along the bottom of the chamber.  I took a 1/2" pipe and drilled 1/4" holes at 10" intervals, 10" from each end (so, 6 holes total).  I machined plates that fit over the fan intake fittings to hold it in place.  This also would help force the introduced air up towards the flame outlets at the top, instead of simply flowing out the open ends.

I ran these at 60 PSI, at pretty high flow rates, and fiddled with the gas to get various effects  Here's what I got at about 30 PSI gas:

The flame isn't very tight, but I'm definitely getting a translation.  At higher PSI, instead of getting a larger flame, it was simply getting spread out further, getting less localized.

I have an idea next to simply improve the ventilation of the sheath by cutting the upper half of the sides off, and seeing if this gives me the desired effect; if it does, then I can possibly reintroduce some shielding by adding sections of 6" diameter HVAC conduit.  The purpose of this is to keep the innards hidden, so that the mechanism isn't obvious.  This is the real issue I'm seeing: if I cut the top off the sheath, this would probably work, but then it would be obvious what the mechanism was, and the aesthetic would kind of be ruined.  So trying to get this to work inside the sheath, or SOME kind of sheath, seems like what I'd like to do.  Possibly going to an even larger sheath, or adding more holes to the top, or all of the above could also help with ventilation and exhaust.  Some progress, but still needs work.