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Has anyone tried arc ignition for black powder engines?

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Jeff Lassahn

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I'm thinking of building an ignition system that uses a spark gap to generate an arc instead of a hot wire.
Has anyone ever tried anything like that? Is it already known to be a dumb idea?
 

mbeels

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I just noticed this on the Apogee website, so apparently it works:

 

DaveW6DPS

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Having a spark that produces enough heat would be difficult, especially one that would fit in (and out) a BP motor nozzle.

You could augment with Pyrodex, but that also works with resistive ignitors.
 

Jeff Lassahn

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That Apogee thing looks a lot like what I was thinking of. Stuff the wire pair up into the engine turn the spark on...

I'm not clear on what's needed to achieve reliable ignition. Is it large heat output, high temperature, or both? An arc will have very high temperature but the total heat energy will be pretty low.
 

Steve Shannon

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Heat transfer - enough to ignite the BP, is what’s necessary. Heat transfer requires both sufficient temperature differential and enough time to get the BP lit. The greater the heat differential the less time is needed.
Years ago, Aerotech made a device that mounted to the ejection charge well and used a spark gap to light BP. I want to say it was an electronic timer rather than baro or accelerometer based.
Electric matches are cheap and easy to acquire. BP is reliable. Better mousetraps are more of a marketing problem than an engineering problem.
 

Steve Shannon

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Heat transfer - enough to ignite the BP, is what’s necessary. Heat transfer requires both sufficient temperature differential and enough time to get the BP lit. The greater the heat differential the less time is needed.
Years ago, Aerotech made a device that mounted to the ejection charge well and used a spark gap to light BP. I want to say it was an electronic timer rather than baro or accelerometer based.
Electric matches are cheap and easy to acquire. BP is reliable. Better mousetraps are more of a marketing problem than an engineering problem.
As I think about it, the Aerotech EDC might have just used a hot wire.
 

DaveW6DPS

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Combustible solids like BP propellant burn very energetically once lit. It does take a significant amount of heat to ignite them reliably.

Having a spark gap essentially packed in actual black powder causes very rapid ignition, and with actual powder the particles are very small. Lighting an ejection charge is quite different than a fuel grain.

As for the Hypertec hybrids, they use a spark gap made from speaker wire with combustible insulation and flowing gaseous oxygen. Again, very different than lighting a fuel grain.
 

RocketRev

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Lighting a black powder ejection charge with a spark is relatively easy as you can get the grains of BP directly in the path of the spark.

Unfortunately, getting a solid propellant fuel grain directly in the "path" of a spark would be very difficult at best. Might be easier to use a spark to light BP which in turn would lite the motor. But getting the BP to hold in one place with the sparker and in contact with the fuel grain at the same time might be harder than it sounds.

Seems just a tad unnecessarily complicated to me.

My brain seems to think that there was a thread once upon a time, about using glow plugs to light BP motors, but I think that I remember that the glow plugs didn't last long from the corrosive nature of the BP fuel. I hope that somebody remembers better than me on this one.......

Brad
 

prfesser

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Fine granular BP such as 4F has a lot of surface area to catch a spark, hence the Lightning Bug. A solid BP propellant grain as in a BP motor may be somewhat hard to ignite reliably.

Best -- Terry
 

rocket_troy

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... and if you have money to burn, you can play with one of these.
 
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OverTheTop

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I think the Apogee thing would probably work if you had the ends of the wires in contact with the motor grain.

... and if you have money to burn, you can play with one of these.
Focusing is usually the problem with this approach. One of the guys on the Australian forum tried this for BP ignition for deployment, through a sapphire window. Don't recall if it ever flew.
 

Jeff Lassahn

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My working assumption is that it goes something like this:

igniter.jpeg

The goal is to raise some small region of the propellant surface above the ignition temperature. The arc itself is much hotter than that, so there's no problem with temperature. The trick is to get enough heat out of the arc to heat up the cold air between the arc and the propellant, and to overcome heat conduction from the propellant surface into the bulk propellant.

It all seems very dependent on lots of practical stuff about the engine materials that I'm not going to be able to figure out in advance.

So I'm thinking I'll just give it a try. Build a spark coil, see how it performs in terms of being able to do things like light pieces of paper or heat up small objects it's in contact with, and if that looks promising try igniting a few engines.
 

Stefan2k4

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Would an ARC not also generate free radicals and ozone? Would that perhaps also make ignition quicker?
 

rocket_troy

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Would an ARC not also generate free radicals and ozone? Would that perhaps also make ignition quicker?
One would think so. They seem to produce more ozone if the conditions aren't right for a noticable spark and more NO2/N2O4 if there is a strong spark but either way, what it produces would likely assist with the reaction with the *fuel* in the propellant.
 

rocket_troy

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Focusing is usually the problem with this approach. One of the guys on the Australian forum tried this for BP ignition for deployment, through a sapphire window. Don't recall if it ever flew.
Maybe. Don't forget though, this is 5W IR. I've ignited dark match heads with a 500mW green laser from say 30cm (albeit with some delay) but yes, you would likely need some kind of focusing.
 

rocket_troy

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So I'm thinking I'll just give it a try. Build a spark coil, see how it performs
Would you really build one when they're everywhere over the internet from China for a few bucks? Mind you, most of them (IMHO) are pretty useless compared to the old Sparkfun variety that consistently produced a spectacular arc. Pity it's discontinued.
 

RocketRev

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From your diagram, it looks like you plan to ignite black-powder Estes type motors. And yes, I know that they are not really "black powder" motors, but it is none the less, the conventional nomenclature for these motors.

Oddly enough, this should make it easier to use your spark to "ignite" your motor.

Have you heard of the old n"flash in the pan" method for igniting BP motor clusters? In essence that's what you could do with your single BP motor and your "sparking device motor igniter." Set up your motor and your "sparking device" exactly like you have them in your diagram. Then all you need to do is add the 4F black powder, like the prfesser Terry suggests, getting the 4F-bp held in place between the "sparking device" and the propellant in the "core" of the motor.

The Sparking device should be able to ignite the 4F-BP and the 4F-BP should ignite the motor itself. I know that its not direct ignition of the motor with the spark, but any direct ignition will be unreliable because of the laws of thermodynamics. You know the difficulty of directing the transference of energy where you want that energy to be transferred rather than where that energy is most easily dissipated into loose heat rather than transferred from sparking device directly to the fuel grain. Using the 4F-bp between the sparking device and the fuel grain will insure a far higher percentage of motor ignitions.

And for whatever reason, every single time I use the word "nomenclature" my brain still instantly goes back to the original b/w film "the Day the Earth Stood Still" to the first "extraterrestrial" phrase I ever learned, "Klaatu barada nikto." As a kid, I thought for sure he was talking about me!

Brad "barada" Wilson
 

caveduck

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Sounds like an interesting project. You can get a *ton* of heat out of an arc with the right parameters. Old time movie lights and projectors were all arc based...they consumed prodigious amounts of electricity and had to use solid carbon electrodes because they ran so hot they would vaporize anything else. Sometimes they even set theatres and movie sets on fire. I'd love to see an arc ignitor that would reliably (99%) start HPR Aerotech composite propellant motors that don't have built-in ignition assist...have seen people burn three $40 BKNO3 ignitors just to get an M motor lit.

IIRC with the high current arcs you had to have adjustable electrode spacing, since they need to be close together to start the arc. Once lit, you have plasma between the electrodes and can pull them further apart since the ionized plasma has much lower resistance. There might be better ways now with a smarter power supply, e.g. use a high voltage pulse to start it up and then bring up the current with lower voltage.
 
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Stefan2k4

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IIRC with the high current arcs you had to have adjustable electrode spacing, since they need to be close together to start the arc. Once lit, you have plasma between the electrodes and can pull them further apart since the ionized plasma has much lower resistance. There might be better ways now with a smarter power supply, e.g. use a high voltage pulse to start it up and then bring up the current with lower voltage.
Yeah, if arcs can be used to weld and cut steel, surely they could be used to ignite a propellant grain. Perhaps a good starting point would be to look at the design of TIG welders or plasma cutters. Also the grain of a black powder motor should be somewhat conductive since it contains carbon.
 

prfesser

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From your diagram, it looks like you plan to ignite black-powder Estes type motors. And yes, I know that they are not really "black powder" motors, but it is none the less, the conventional nomenclature for these motors.
Hi Brad, my understanding is that Estes actually uses commercial Meal D blackpowder for the propellant, for consistency. I don't know about the delay charge, but from a pyrotechnic standpoint it probably contains a large excess of sulfur and less KNO3, similar to gopher gassers. The SDS for their motors says 60-80% KNO3, 10-20% sulfur, 10-20% charcoal. That's probably an average composition of propellant + delay for all size motors and delay charges.

Best -- Terry
 

RocketRev

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Hello Terry,

Obviously you're right about the composition of Estes propellant. Who would know better? My point about Estes motors is that the "black-powder" that Estes is using is not the same thing as the BP that we often use for recovery device deployment charges with our electronic in our Av-bays. Its not the same thing as cramming a bunch of Dupont 2F, 3F, or even 4F into an empty motor case and calling it "propellant." Chemically they have mostly the same ingredients, but in differing proportions thus creating a propellant rather than low explosive. Am I saying that well enough? Or am I completely in left field?

Brad
 

PatD

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Hello Terry,

Obviously you're right about the composition of Estes propellant. Who would know better? My point about Estes motors is that the "black-powder" that Estes is using is not the same thing as the BP that we often use for recovery device deployment charges with our electronic in our Av-bays. Its not the same thing as cramming a bunch of Dupont 2F, 3F, or even 4F into an empty motor case and calling it "propellant." Chemically they have mostly the same ingredients, but in differing proportions thus creating a propellant rather than low explosive. Am I saying that well enough? Or am I completely in left field?

Brad
I would say pretty right. The proportions define the reaction. Lower oxidizer fuels burn more slowly in general.
 

PatD

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Hi Brad, my understanding is that Estes actually uses commercial Meal D blackpowder for the propellant, for consistency. I don't know about the delay charge, but from a pyrotechnic standpoint it probably contains a large excess of sulfur and less KNO3, similar to gopher gassers. The SDS for their motors says 60-80% KNO3, 10-20% sulfur, 10-20% charcoal. That's probably an average composition of propellant + delay for all size motors and delay charges.

Best -- Terry
With that wide a variation I would guess it's an attempt to disguise the formulation. When I was doing amateur pyro my mixes were always really close to the formula. I do know that commercial production of the mixes I saw were large and measured by scoop. :oops:
 

prfesser

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Hello Terry,

Obviously you're right about the composition of Estes propellant. Who would know better? My point about Estes motors is that the "black-powder" that Estes is using is not the same thing as the BP that we often use for recovery device deployment charges with our electronic in our Av-bays. Its not the same thing as cramming a bunch of Dupont 2F, 3F, or even 4F into an empty motor case and calling it "propellant." Chemically they have mostly the same ingredients, but in differing proportions thus creating a propellant rather than low explosive. Am I saying that well enough? Or am I completely in left field?

Brad
All the different sizes from FA to X-fine Meal are made from the same batch. After thorough mixing the powder is "corned"---pressed into cakes and allowed to dry, then broken up---and sieved into the different sizes. I think they may tumble each batch to round off the edges and give more uniform particles, and they get a coating of some sort.

The finer stuff like Meal D requires less pressure to consolidate it into a propellant grain. Finer grades could be used but I'd guess that they're even more sensitive to spark than Meal D.

Fireworks enthusiasts often use a similar method, but the mixture is higher in coarse charcoal to give a nice tail. Such mixtures usually burn much more slowly, so their rockets are almost always coreburners, for maximum thrust.

I'm not certain where I saw the statement that Estes uses Meal D as the propellant. Memory again... :dontknow:

Best -- Terry
 
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