NiCrome "hotwire" Ignition for Propane Flame Effects

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Introduction: NiCrome "hotwire" Ignition for Propane Flame Effects

About: Just your average robotics and fire arts tinkerer.

I'm going to give a run-down of the nicrome ignition system (aka Juniper) that we used on 2PiR this year.

2PiR uses high velocity, high speed, computer sequenced effects. Because of these traits, it is poorly suited for more conventional pilot flames, such as the low pressure stainless steel wool style or the bernzomatic torch type. If you are making a flame effect for anything that is not high-repetition, high velocity, and terrible on pilots, please consider a different style of pilot than hotwires.

Reasons for using NiCrome:
-Can be extremely reliable
- Won't blow out: good for use in areas you can't access easily
- Can ignite extremely short bursts somewhat more reliably than "orange flame" pilots (this is a debatable point, keep in mind that we started using NiCr wires as a last resort)
- It can look really cool if done well

Reasons to not use NiCrome:
-You need between 9 and 12 amps to get it to autoignition temperature (for propane), at 120 volts, that is a whole bunch of watts. This style is not recommended for generator use.
- You will need to either get a power supply that is 12v x (effects * 15) amps if you are running the ignitors in parallel. If you run them in Series, you can run a bunch (we got 16) on one circuit, but you have the Christmas Lights problem if anything goes wrong.
- They need to be protected very well from shorting to the chassis or shocking bystanders (more on this later)
- It's way overkill for most effects
- The wires look like the inside of a toaster, and that's uncool.

Step 1: Me Talking You Out of Using NiCrome

So if you are reading this, you have probably built a flame effect or two. If you really haven't gotten deep into ignition woes, just quit reading here and don't worry about stuff like this. Normal, dumb, steel wool and 1/2 psi propane will work amazingly well for making a yellow flame that will light just about anything.

If you are doing something for an art car or whatever, just know that from here until the finished project was (for us) around 80 man hours, 4 priority shipments from McMaster, and a whole lot of wasted money. Your mileage may vary, but using a system like this will be amazingly expensive and time consuming compared to more conventional pilots.

Step 2: Jank

Now's when you make a totally shitty prototype just to prove that it will work on your application. You will need Nicrome wire! You will need Power! You will need your ready-to-fire flame effect.

Nicrome: McMaster parts:
.0359" Diameter
1/8 lb. Spool 8880K75 $8.10
1/4 lb. Spool 8880K16 15.77
1 lb. Spool 8880K46 47.94

We got a pound, it's a whole lot. We've used around 50 feet of the spool we got, and have hardly made a dent in it. I'd suggest gettin' the q.p.

You'll also need some way of connecting this to power. At this point, you'll probably just want to do the easy thing, screw-lock it onto the business ends of some 110, and I don't blame you, but first, coil it. Coiling seriously increases the efficiency of the hotwire by an amazing amount, because the heat bounces around the inside of the coil and also compresses the air in there, giving you more heat for less.

To coil well, get a wood screw or a coarse thread machine screw, and wrap your wire tightly around it, then unscrew the screw out of the middle.

Once you've got a length appropriate for your application (around 9.0-15.0 Ohms for 110v, depending on how serious your effect is), you'll need to place this NEAR the stream of propane. Don't put it right in the middle, or it will get "blown out" by the cold propane, and never achieve autoignition temperatures while mixed with oxygen.


That's our test rig in action, and also why it's called "Juniper". We made NIMBY smell like a gin factory.

Step 3: Stand + Infrastructure

So now you've lit propane with a glowing wire. That's not useful at all unless you've got some sort of stand, and you can do it in a nice manner.

Your stand needs to
-Shield the nicrome from wind. Nicrome is EXTREMELY wind sensitive
-Be okey with being bathed in flames. your metal will get very hot, since it is inside fire.
-Be able to transmit power to the nicrome and not disintegrate at hot temperatures.
-Be adjustable: The point where your column of propane is ignitable is dependent on pressure, altitude, and the will of god, so you need to be able to adjust each ignitor both into and out of the column, but also towards and away from the nozzle.

You will need at some point heat resistant wires. Copper conductor wires are completely unsuitable for this application, and they will vaporize, leaving a cool greenish residue on the nicrome coil. This is less than optimal.

I'm going to explain things with the pictures and captions here.

McMaster part numbers:
Ceramic tube "thermeez"
88175K31 $14 for 25 feet
heat insulated wire: 800 degree rated, 14 gauge.
8209K17

And probably the most dangerous thing I've used in a while, is KOPR-Shield, a copper suspension that reduces the resistance of plugs by a phenomenal amount. Our system used drop cords to connect the different ignitors together, and we were getting an extra 7Ohms from the plugs! (Cheap home depot shit), so with this Kopr Shield we reduced that to .5 Ohms!!! The downside is that any stray bits of this conduct better than wire, and it's only slightly safer than throwing all your electrical cables in a puddle of water.

Step 4: Shielding

If you put these right in the stream of propane, the fuel cools down the coil, and there is no fire, only suck. The second snag is the mount points for the nicrome. Most ways of joining two wires (like screw terminals) have a bottleneck, where things will get really hot and disintegrate. Well, not in all electronics, but they will here. Also, you don't want to shock people.

We positioned the ignitors at the edge of the flame (as seen in the pics from Fire Arts Festival), but also obscured them behind a perfsteel cage. To make this, we made a + sign of perfsteel, then hammered it together. It not only breaks the speed of the fuel, but also hides the fact that our ignitors are glorified toaster bits.

To get around the melty bit, we had one of our very skilled people, Ian Baker, tig weld the nicrome wire to some nuts, and then we bolted the 14 gauge thermal wire to those. After we did that, we had no failures that weren't a result of our own sillyness.

The safety measure that you really want to get in here is keeping these live wires from shorting to ground and either electrocuting people or causing mayhem. We got around this by grounding all the chassis to the ground wire of our 3 prong power, and putting the thing on a GFCI circuit. Then, because I'm paranoid, I taped a screwdriver to a 2x4 and grounded the thing, the GFCI blew, which was a good test, because about 6 days later, I accidentally stuck a screwdriver across those, and didn't feel a shock at all. GFCI's are great stuff.

I so seriously need to sand down and paint all of those, but even Bar-B-Que black will get cooked off... I guess this is a work-in-progress then.

Step 5: BURNINATE!!!



enjoy.

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    33 Discussions

    I would like to build a small propane flame projector to use onstage while rock band playing.

    we've used alot of other effects in the past; volcano's gerbs, waterfalls, cannons ect

    now we're looking for instructions on building propane flame projectors the will only be used outdoors for added safety.

     That is just fantastic! Thanks for sharing your experience and writing this up! You'd think it would be easier to make fire, eh?   2 pi r rox!

    Great Trogdor reference there.

    I see that you've got the tanks on their side. You do realize that this could cause a potential problem, because liquid can cause a backflash. Also, propane is heavier than air, which means any escaping vapor, or leaks will hang at ground level, so if you have a stray spark, you've got yourself a problem.

    3 replies

    Those aren't our tanks. Those are our vapor accumulators. They contain no liquid (assured now, since we regulate down from tank pressure). Liquid there would be disastrous for our valve diaphrams. I'm unfamiliar with this backflash scenario, but in terms of escaping vapor, we leak test our system at all plumbing after initial setup, and check all the QR's or any other adjusted fittings before any run. We are generally running these at events where having leaking raw propane is unacceptable (as even though it is smellable at 1/100 flammable concentration, it gives the appearance of carelessness).

    I need help igniting propane for a a stunt limo I built. I added a propane tube to the side of the limo to make it appear on fire. Can you help?

    Yeah!!!!!!!!!!!!!!!!!! FFFFFFFIIIIIIIIIIIIIIIIIIIIIYYYYYYYYYYYYYYAAAAAAAAAAAHHHHHHH!!!!!!!!!!!!!!!!!!!! Tetranitrate, you need to ship me everything pyro related! All hail the fire king! Lol, this instructable is cool though...

    I'd rather write my entire life story than try to document any of the eight or nine major systems of DDI. It's so terribly complex, I'd get lost just starting. Also, DDI existed two years before I got involved with this group, I've just been involved with small systems of the whole. Also, insert some cop-out about trade secrets of artists here.

    used nicrome is twitchy at best. You can use old nicrome, but the stuff in toasters has really low coil density, so it isn't going to heat up as well. It is also designed for a duty cycle of about 5 minutes, and not to be immersed in flames. The idea of Nicrome is to make an elegant ignitor solution, it is expensive to do right.