What makes motor flames colored?

I saw in one of the Aerotech announcement topics that they are coming out with a green propellant. What makes the flame green? This got me thinking... what makes red, blue, etc? I think I need to get to a launch in the US to see some of these things! Mostly white and smokey here.

TJMcB

Colored flames are the result of chemicals, generally metals, added to the propellant that give off a certain color of light when burned. For example, strontium gives a reddish color when burned. It really adds nothing to the power - it's pretty much all for looks.

Green is from barium compounds (kinda toxic). Some people like the affects, other people would rather have the higher efficiency without the additives.

Oh, and blue is from copper oxide. A little on the wild side.

Originally posted by cjl
Colored flames are the result of chemicals, generally metals, added to the propellant that give off a certain color of light when burned. For example, strontium gives a reddish color when burned. It really adds nothing to the power - it's pretty much all for looks.

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Generally metals are used however the example given (strontium) while a metal, strontium nitrate is not. Also strontium nitrate which most of the people I know use is an oxidizer so it's not "all" for looks. Most of the guys I know with an exception or two are not high fliers, especially here in the east so a wide variety of motor are flown without worries of bonking the waiver.

Bonk the waiver?

How does one do that?

Is that like bonk the monkey?
Bonk the chicken?

Originally posted by Bahaska
Bonk the waiver?

How does one do that?

Is that like bonk the monkey?
Bonk the chicken?

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Like bonking your pointy head on a ceiling that's too low.

Theoretically, you can manipulate the flame color while increasing Isp. This would mean using say, a perchlorate or even a nitroformate salt of the metal.

Blue from Cu
Red from Sr
Green from Ba
Purple would be from K traditionally, but maybe a Cr or Co could lend a helping hand.

a skidmark is from titanium flakes in the propellant, that is why it usually is pricey.

Originally posted by Terry McB
I saw in one of the Aerotech announcement topics that they are coming out with a green propellant.

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Are you sure you didn't see in that topic that people were wishing that AT would come out with a green propellant?

Chicagonative wrote

a skidmark is from titanium flakes in the propellant, that is why it usually is pricey.

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Hmm. The 38mm I315 Skid is the same price as the other 38/640 motors. I think the same is true for larger motors.
(checks) Okay, there's an $8 premium for the K555SK over the other similar-sized 54mm motors, but otherwise they're the same price.

Of course they've got significantly less total impulse than the other motors, so you're trading flash for performance.

I recently made and tested some propellant with cast iron
shavings. For night flying it has a great orange color with lots of
orange sparks. Not as bright as the Skidmark's (titanium) but still
cool and less dangerous to work with.

William

I hope the new regulations for chemicals doesn't effect the hobby.

Originally posted by chicagonative17
a skidmark is from titanium flakes in the propellant, that is why it usually is pricey.

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Just wondering what creates the classic crackling sound of a Skidmark motor?

Thanks,
Ken

Originally posted by spikeyken
Just wondering what creates the classic crackling sound of a Skidmark motor?

Thanks,
Ken

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When you have hot metal sprks flying out of a nozzle at supersonic speeds it can create a crackling sound. The larger they are the louder it is

Ben

Thank you everyone for the information. This is interesting stuff!

And now, a moment of science....

Almost any molecule, when heated sufficiently, will give off light at particular frequencies. Different substances emit light at different frequencies, depending on exactly how much energy it takes to move their electrons between different energy levels.

Astronomers make use of this fact to identify what elements are present in distant stars, and chemists do "flame tests" to identify unknown substances. A sophisticated version of the flame test, the "Gas Chromatograph Mass Spectrometer", or GCMS, is used in many labs to identify substances by their light emission "fingerprints".

Fireworks makers have discovered over the past few thousand years that the brightest, purest, and most intense colors tend to come from chlorine salts of various metals. For example, Strontium Chloride emits a very bright red color when heated in a flame. Barium Chloride is intensely green, and so on.

Unfortunately, if you just add a metallic chloride to an existing propellant, it generally won't burn as well; chlorine is a powerful oxidizer (better than oxygen...), but it is already tightly bound with the metal, and the addition of your metallic salt takes away space that could have been filled, instead, with ready-to-react fuel and oxidizers.

The usual solution is to add a more-reactive compound of the metal (such as a carbonate, or better yet, a nitrate), along with some form of "chlorine donor" -- a fuel or oxidizer that will release excess chlorine when it reacts in the motor. Chlorinated plastics and rubbers, such as PVC or Parlon, are often used as chlorine-donor fuels, and chlorinated oxidizers, such as Ammonium Perchlorate, are also decent chlorine donors.

Finding combinations of "ingredients" that produce the desired physical properties in your propellant -- flame color, burn rate, pressure exponent, smokiness or clarity of exhaust, sparks, smooth burn, shear strength and durometer when cured, viscosity when mixing, etc. -- is quite the chemical engineering challenge. My hat is off to the many commercial manufacturers and talented amateur propellant researchers who have risen to the challenge, and given us the great variety of propellant choices that we have.

Thanks, guys!

- Rick "impressed" Dickinson

What the heck is going on here?!?

This is the third informative thread I've read on here this morning! we're actually getting into some legitimate discussions finally! woot!

Catocene- with a name like that I certainly don't doubt your expertise, but I have a hard time seeing how adding a chemical to your motor can increase ISP. NH4ClO4 is an amazingly powerful oxidizer, and anytime you remove a percentage of AP to replace it with a different metal (oxidizer or not) you're going to subtract from the overall performance of the motor.
Please, correct me if I'm wrong....

Originally posted by Nate
What the heck is going on here?!?

This is the third informative thread I've read on here this morning! we're actually getting into some legitimate discussions finally! woot!

Catocene- with a name like that I certainly don't doubt your expertise, but I have a hard time seeing how adding a chemical to your motor can increase ISP. NH4ClO4 is an amazingly powerful oxidizer, and anytime you remove a percentage of AP to replace it with a different metal (oxidizer or not) you're going to subtract from the overall performance of the motor.
Please, correct me if I'm wrong....

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You're wrong. (How's that for service?)

But seriously, you're mostly right, with one minor caveat: oxidizer content is not the only important variable. It's by far the most important one, but there are others.

If you look through any of the standard reference texts (Sutton's _Rocket Propulsion Elements_, for example), you'll find that quite a bit of (largely government-sponsored) research has gone into optimizing APCP performance in terms of maximizing Isp.

For propellant using common polybutadiene (HTPB or PBAN) binders, you actually get the highest Isp by including a small amount of metal powder -- typically Aluminum, magnesium, or magnalium (an Al/Mg alloy) -- in addition to the AP and binder/fuel. I don't have it in front of me, but I seem to remember the optimum ratio being somewhere around 70/17/13 for AP/Al/PBAN. I'll look it up at lunch (my copy of Sutton is out in my truck).

The metal powder increases the flame temperature, opacifies the propellant, and also serves as a fuel, itself. Higher flame temperature usually means more complete combustion *inside* the motor, which means less fuel is wasted *outside* the motor. Also, higher temps mean higher kinetic energy of the gas molecules, which translates directly to more thrust.

To ensure that combustion takes place only at the surface of the grain, the grain needs to be opaque to the infrared radiation due to the combustion. A mixture of *just* AP and PBAN or HTPB is translucent; usually an opacifier such as lampblack must be added to prevent catos from the whole grain trying to ignite all at once. Metal powder replaces the low-molecular weight lampblack carbon with a denser Al or Mg, improving volumetric loading (basically a measure of overall density, including the empty space in the motor core), and giving a more-reactive fuel with a higher flame temperature.

It's also possible to substitute even-more-reactive ingredients for some of the AP to get even slightly-higher performance propellants. However, this is typically only done for specific military purposes, as the ingredients in question tend to be extremely hazardous, either in terms of stability, toxicity, or both. Most are high-order explosives, like nitroglycerine, RDX, etc.

For amateur and commercial rocketry purposes, AP is just about the best possible solid oxidizer, and the various rubber binder chemicals like PBAN and HTPB have excellent physical and chemical properties for propellant use. APCP with AP/Al/Binder gives just about the highest performance you can get without significant compromises in other areas.

(Of course, so-called "knob" motors, which are designed for effects like colored flames and sparks, rather than pure performance, are another kettle of fish entirely....)

- Rick "Flame on" Dickinson

Originally posted by RocketRick


(Of course, so-called "knob" motors, which are designed for effects like colored flames and sparks, rather than pure performance, are another kettle of fish entirely....)

- Rick "Flame on" Dickinson

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Reported....




I kid...




But you prolly shouldn't say that word. It's bad. People have been banned for it...


I think


One guy's name doesn't say 'banned' under it. Is he really banned?

Originally posted by RocketRick
(Of course, so-called "knob" motors, which are designed for effects like colored flames and sparks, rather than pure performance, are another kettle of fish entirely....)

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But that was what I was asking about originally. It sounds tricky to get the best performance with these additives. Is any one color better than others in this regard?

I'd ask about the "knob" reference, but from what I've seen here lately, I don't dare!

TJMcB

Originally posted by Todd Moore
Reported....


But you prolly shouldn't say that word. It's bad. People have been banned for it...

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Really? Seems silly, to me. What's bad about it?

I've heard the term used many times in a propellant chemistry context, and I've always thought it evoked a fantastic metaphorical image:

I always picture a stereotypical propellant chemist, wearing a white lab coat and goggles, clipboard in hand, standing in front of a big "Propellant Control Panel" festooned with dials, gently tweaking knobs to "turn up the green color", "back off a little on the smoke", etc.

It's wonderfully evocative imagery, and it's actually not too far off, philosophically, from the real-world feedback loop of "design-->test-->evaluate-->re-design" that is common in engineering.

To each his own, eh?

- Rick "Shall I turn down the 'knob' knob for my posts?" Dickinson

Originally posted by Terry McB
I'd ask about the "knob" reference, but from what I've seen here lately, I don't dare!

TJMcB [/B]

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My one, and most likely only, post. A history lesson, if you will.

https://groups.google.com/group/rec...cebd6/ec6212fc8106ba0b?tvc=1#ec6212fc8106ba0b

Originally posted by Terry McB
But that was what I was asking about originally. It sounds tricky to get the best performance with these additives. Is any one color better than others in this regard?
TJMcB

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From what I've seen, the colored propellant that gets the "best" performance is a pale blue color (think Aerotech Blue Thunder, or similar). These usually use a very small quantity of Cupric Oxide, which acts primarily as a burn-rate enhancer, but has the side-effect of making a nice blue flame in APCP propellants.

It takes a *very* small amount of CuO to get the effect desired, which is probably the main secret to its high Isp. You're not replacing 15-20% of the mass with "color stuff" (like you would to get a nice rich green or red), you're replacing well under 1%, and often as low as 0.1% or so. That's literally down in the measurement noise, as far as total specific impulse reduction goes....

- Rick "minor tweak to the formula knob" Dickinson

Thanks again guys. I am actually learning something here!

The term "knob motor" makes sense now. A simple way to refer to propellants with effects and people who like them. Not sure how that could be a bad thing.

Are there examples of formulas on the web? I know the rules say they can't be posted here, but are you allowed to point to where I can find an example?

TJMcB

Very interesting, I never thought that using the word knob would start such a rukus.

Not like someone was threateningsomeone with bodily harm or calling them something worse (wont type it cause ma is watching me)

The term was being used as a form of personal attack against another member, which is why it was causing threads to get pulled.

Subsequently, certain members decided to make it their sole goal on the forum to antagonize the admins and moderators of the forum and are no longer welcome as a result. While I know it's a very popular tack to lay it all on me, the actions taken were put to a vote and there was not a single dissenting vote among the admins and moderators.

We don't get paid for this, so we decided that we weren't getting paid enough to put up with it, and, rather than ditch the whole thing for 3 or 4 people who couldn't wrap their heads around the concept of a moderated forum that has rules about personal attacks, we, as a group, decided to remove the 3 or 4 people who were purposely creating problems.

Please refrain from posting motor composition percentages here. This is covered by TRF's policies on EX discussions.

put my post back please. Remove the percent if you must, but I'd like my post to remain.

Nate,

You post quoted the member post that was pulled, so it will remain pulled as we try to refrain from editing posts. You can, however, repost your comments if you wish.

Carl

I didn't realize how much was trimmed from this thread. My posts would be irrelevant now, so I guess I'll pass.

Originally posted by KermieD
Please refrain from posting motor composition percentages here. This is covered by TRF's policies on EX discussions.

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I apologize for my accidental transgression. I am rather flummoxed, however, by the idea that a discussion of an on-topic technical nature in a "Propulsion" forum would fall afoul of the rules.

I can understand making a decision to avoid posting "recipes" for cookbook-style manufacture of energetic compositions. There's a large potential for misuse of that sort of information by children, and I understand wanting to avoid attracting the usual "basement bomber" types to this forum.

However, I wasn't doing anything of the sort. I was simply correcting some slightly misremembered numbers (which I had previously cited) from a textbook that's probably available in the library of just about any college that offers a chemistry and/or an engineering degree. My post that I was correcting was an answer to a legitimate question about whether or not having anything other than oxidizer and fuel/binder in the rocket fuel would reduce its performance.

Nothing I said would, in any way, "help terrorists" or even promote the making of motors by the unskilled and/or stupid. If anything, pointing out the standard reference texts one ought to read before getting started (Sutton's _Rocket Propulsion Elements_, for example) would tend to have the opposite effect: better-informed and educated people tend to be much more circumspect when it comes to engaging in potentially dangerous activities.

In any case, I'll refrain from mentioning specific percentages in the future.

- Rick "Switching that knob to OFF" Dickinson