Flame color

[wg_bent]

I know that on a gas torch the blue is the hotest part of a flame (welding, soldering etc...) but with a wood stove I notice that some woods seem to produce an instantly blue flame while others produce a bright yellow, others a mix.

Is the color of the flame indicative of temp with a wood fire or is this due to the chemical make of of the wood?

I know in almost all cases, once the wood goes to coal stage, the flames are almost all blue.

 

[babalu87]

I think you answered your own question:

once the wood goes to coal stage, the flames are almost all blue

Blue is hotter than orange is hotter than yellow but the yellow has more heat

Interesting read:

(broken link removed to http://www.straightdope.com/mailbag/mhotflame.html)

I'll try to make this answer worth the wait. Analysis of a flame can be quite complex. Coal and solid fuel flames (my specialty) are the most complex, followed in difficulty by liquid fuel flames, and finally gaseous fuel flames. I'll assume that for your backyard experiments with the wife you're using a butane or propane lighter with a simple gas flame. That means we're dealing with a premixed laminar flame – in lay terms, "a flame that has its fuel mixed with air before burning and a relatively steady shape."

Maybe we should get him on board?

What I'm telling you is that your wife is technically right. The blue part of the flame is the hottest, not the white part. But a manly man is more concerned about the real world – as we saw above (show her the graph), there's more total heat in the tip of the flame, so that's the part you want to use to light the fire. In other words, while she's got a better grasp of theory, you're going to get the fire lit sooner. I'm not saying you won't get an argument as far as your bet goes. But put it to her this way: The price of clean laundry is raw steak.

 

[jimkelt]

We had some scary pellets about nine years ago that gave off purple , and yellow flames. You could see bits of plastic and debris in the pellets, I even found little bits of metal a few times. Found out later they were using old pallets-Yikes!

 

[DoubleClutch]

I think when you see blue flames when burning wood, you're seeing gases (like gaseous sap, sugars, alcohols, etc) burning that are high in hydrogen.

Yellow flames commonly show a lot of carbon, rather than hydrogen, burning.

I think when you throw dry wood onto a fire, it gets hot, then the sugars and sap and alcohols all vaporize and burn -- producing blue flames -- and as those components of the wood are burned off, the fire becomes more yellow as carbon, rather than hydrogen, becomes the predominant fuel burning.

That's my theory, anyway, and I'm sticking to it!

 

[wg_bent]

I think when you see blue flames when burning wood, you're seeing gases (like gaseous sap, sugars, alcohols, etc) burning that are high in hydrogen.

Yellow flames commonly show a lot of carbon, rather than hydrogen, burning.

I think when you throw dry wood onto a fire, it gets hot, then the sugars and sap and alcohols all vaporize and burn -- producing blue flames -- and as those components of the wood are burned off, the fire becomes more yellow as carbon, rather than hydrogen, becomes the predominant fuel burning.

That's my theory, anyway, and I'm sticking to it!

But that's backward of what I observe. if I have nothing but coals I usually have short 1-2 inch high almost purely blue flames. Maybe just a touch of yellow.

Toss in an oak or elm split..Lots of big blue flames. Toss in a pine or sumac split...a massive amount of yellow. Hard to tell which puts out more heat in the first 10 or so minutes of fire, both are capable of a lot of heat. Eventually, coal becomes coal, and the flames return to little blue dancers. Most often, secondary can a mix of blue and yellow or even deep orange.

so far, Not sure we have a compelling position. Sorry DC...

 

[spot]

If you want to purposely color your fire (ooh!-pretty!) ...then dissolve one of these chemicals in water, soak a log in it, and let it dry.

Orange ---------Calcium Chloride (a bleaching powder)
Yellow ----------Sodium Chloride (table salt)
Yellow-Green---Borax (a laundry powder)
Green-----------Copper Sulfate (for swimming pools)
Blue-------------Copper Chloride
Purple-----------Potassium Chloride (fertilizer)
White------------Magnesium Sulfate (Epsom salts)

Use only one chemical per log (mixing will not produce "multiple colors")
however, you may put more than one type of "colorized log" in the fire at once.

Instead of big logs, you can use pinecones or sawdust.

CAUTION!! (you knew there would be one)
Some of these chemicals are not very pleasant to get all over yourself, your clothes, the living room, or the dog. Use proper precautions (goggles etc.)

 

[Gooserider]

I think at least some of the answer may be further down in that post from Straight Dope that babalu87 was pointing at:

Apart from incombustible elements, the color of a hydrocarbon flame is primarily dependent on the richness of the flame – that is, on how much oxygen there is to combust the fuel. In practice*, when the mixture is slightly lean (has more oxygen than required for complete combustion), the color of the combustion zone is generally blue-violet due to large amounts of high-energy radical carbon and hydrogen compounds. When the mixture is slightly rich (slightly too much fuel and not enough oxygen), the color is sometimes green due to C2 molecules breaking free, and the high-temperature products can glow red from the CO2 and H2O produced during combustion. When the mixture is very fuel rich (a poor flame, with not enough oxygen to burn properly), carbon particles form and an intense yellow radiation results from their being heated in the flame. In very rich flames – often you see this in candles – soot particles may impart a black color to the outer edge of the yellow flame.

This would suggest to me that the logs putting out yellow flames are outgassing more, giving a richer mixture than the logs putting out less gas at any given moment (assuming the air inlet is the same setting)

This would be consistent with the notion that softwoods burn hotter but faster (more gas for a shorter time) and put out more creosote (less complete combustion due to insufficient air in the mix) Once the initial gas is burned off and you are down to coals, then you will see blue flames because you now have plenty of oxygen, with the flame size being limited by the amount of fuel gas coming off the coals....

This is just theory, but it seems to fit to a first approximation.

Gooserider

 

[begreen]

I noticed this when getting really good secondary combustion. You can see it in the video with the Idaho Energy logs. As they start off the flame is yellow. Then I damper down and with the logs about 75% involved, the flame is blue. Finally with the logs fully involved and the air intake closed off, they go towards a whitish yellow with blue tinges. Really cool to watch.

https://www.hearth.com/talk/threads/6247/

 

[wg_bent]

I think at least some of the answer may be further down in that post from Straight Dope that babalu87 was pointing at:

Apart from incombustible elements, the color of a hydrocarbon flame is primarily dependent on the richness of the flame – that is, on how much oxygen there is to combust the fuel. In practice*, when the mixture is slightly lean (has more oxygen than required for complete combustion), the color of the combustion zone is generally blue-violet due to large amounts of high-energy radical carbon and hydrogen compounds. When the mixture is slightly rich (slightly too much fuel and not enough oxygen), the color is sometimes green due to C2 molecules breaking free, and the high-temperature products can glow red from the CO2 and H2O produced during combustion. When the mixture is very fuel rich (a poor flame, with not enough oxygen to burn properly), carbon particles form and an intense yellow radiation results from their being heated in the flame. In very rich flames – often you see this in candles – soot particles may impart a black color to the outer edge of the yellow flame.

This would suggest to me that the logs putting out yellow flames are outgassing more, giving a richer mixture than the logs putting out less gas at any given moment (assuming the air inlet is the same setting)

This would be consistent with the notion that softwoods burn hotter but faster (more gas for a shorter time) and put out more creosote (less complete combustion due to insufficient air in the mix) Once the initial gas is burned off and you are down to coals, then you will see blue flames because you now have plenty of oxygen, with the flame size being limited by the amount of fuel gas coming off the coals....

This is just theory, but it seems to fit to a first approximation.

Gooserider

I think your close Goose. "insufficient air in the mix" Mix being the operative word. Wood stoves have something like 200 -300 % more oxygen than they need, but may not mix the gasses optimally in a large offgassing situation.

Where are the pros here? We need the guys from Englander to weigh in here. I'll bet they know exactly why. (is that an obvious bait or what?)

 

[DriftWood]

So is less wood in a fire box 1/4 full a better way to lean out the fuel for a hotter flame in a cold box.

 

[Gooserider]

So is less wood in a fire box 1/4 full a better way to lean out the fuel for a hotter flame in a cold box.

I wouldn't think so, as I'd suspect that the result would be hotter flames, but less of them for a net result of fewer BTU's being released.

Presumably the standard instructions are the optimal approach - remember that they have been empirically developed by experimentation, which always trumps theory.

Our smoke dragon burns differently than a modern stove, but still seems to come up to temp fastest when I put a full load in it, rather than partially filling it. I do put kindling and paper in the cold stove, but that is just to bridge between the match and the splits - it's the splits that make the heat.

Gooserider