What constructs a flame?

Hi Caleb,

Consider this description from Wikipedia:

"Flaming fires involve the rapid oxidation of a fuel (combustion or release of energy) with associated flame, heat, and light. The flame itself occurs within a region of gas where intense exothermic reactions are taking place. An exothermic reaction is a chemical reaction whereby heat and energy are released as a substance changes to a more stable chemical form (in the case of fire, usually generating carbon dioxide and water). As chemical reactions occur within the fuel being burned, light is usually emitted as photons are released by the oxidation of the fuel. Depending upon the specific chemical and physical change taking place within the fuel, the flame may or may not emit light in the visible spectrum. For example, burning alcohol or burning hydrogen are usually invisible although the heat given off is tremendous.

The visible "clear" flame has no mass. What we see as a flame is actually energy (photons) being released in the form of light by the oxidation of the fuel. The color of the flame is dependent upon the energy level of the photons emitted. Lower energy levels produce colors toward the red end of the light spectrum while higher energy levels produce colors toward the blue end of the spectrum. The hottest flames are white in appearance. The color of a fire may also be affected by chemical elements in the flame, such as barium giving a green flame color. The flame color depends also on the unoxidized carbon particles. In some cases there is a partial fuel oxidation due to insufficient oxygen in the central part of the flame where combustion reactions take place. In such cases the unoxidized hot carbon particles emit radiation in the light spectrum, resulting in a yellow/red flame, such that of common house fireplace."

Does this answer your question?

I am anticipatinig that you are especially interested in flames from wood fires.

Basically, once a wood fire is going, the heat boils volatile gases from the wood, which rises and ignites just above the wood. The burning, escaping gases are responsible for the dancing flames.

From How Stuff Works http://science.howstuffworks.com/fire1.htm :

Here's the sequence of events in a typical wood fire:

• Something heats the wood to a very high temperature. The heat can come from lots of different things -- a match, focused light, friction, lightning, something else that is already burning...
• When the wood reaches about 300 degrees Fahrenheit (150 degrees Celsius), the heat decomposes some of the cellulose material that makes up the wood.
• Some of the decomposed material is released as volatile gases. We know these gases as smoke. Smoke is compounds of hydrogen, carbon and oxygen. The rest of the material forms char, which is nearly pure carbon, and ash, which is all of the unburnable minerals in the wood (calcium, potassium, and so on). The char is what you buy when you buy charcoal. Charcoal is wood that has been heated to remove nearly all of the volatile gases and leave behind the carbon. That is why a charcoal fire burns with no smoke.

• The actual burning of wood then happens in two separate reactions:
• When the volatile gases are hot enough (about 500 degrees F (260 degrees C) for wood), the compound molecules break apart, and the atoms recombine with the oxygen to form water, carbon dioxide and other products. In other words, they burn.
• The carbon in the char combines with oxygen as well, and this is a much slower reaction. That is why charcoal in a BBQ can stay hot for a long time.

Fire emits light and heat , fuel , any kind oil based , wood ,plastics , gases when burn in atmosphere creats a flame depending upon amount burned , it can be described as photons emited that you notice with your eyes, you are only 14 years and your observations are worth noting ,good.

you can observe sparks emitting from friction at grinding , rubbing ,impact at various places workshops , fabrication shops , factories if you are allowed. what causes sparks may be something is burning due to excessive heat due to chirping of fine flyoffs of material being process you see light , sparks flying off , here meterials being processed work like fuel that heat to obeservable light

In the flame, what you are seeing is not any different than what you see when you turn on an incandescent lamp, normal light bulb. From the flame comes microscopic pieces of carbon that are so hot they glow just like the light bulb, these carbon pieces are what turn the chimney black and your hands if you rub it inside the chimney.

"the flame comes microscopic pieces of carbon that are so hot they glow just like the light bulb"

My understanding is that the glowing carbon particles account for the orange part of the flame. The blue part of the flame comes from burning methane and similar gases without carbon contamination, similar to the flame in a gas appliance. Since I am not a chemist, corrections and clarifications from someone more knowledgeable would be appreciated.

That's the way I recall it too. With the hottest (highest heat intensity) occurring at the tip of the blue cone.

But it has been a few years. I recall an experiment in which we water soaked kitchen matches overnight and then timed how long it took a match to ignite when placed at specific points within the flame.

What realy happens is that the gasses, which are heated and in a raised or agitated state, have electrons jump to a higher level in the atoms structure during the burning process. The flame occurs when these gasses then cool down again when they fly away from the fire, These electrons will jump back to their proper position which releases the energy stored in them whilst in the raised state. This energy release is emited as light.

Anything else said about particles is bs. A flame has no particles in it unless you believe that photons are particles, which some scientists say they are.

Your right the flame does not emit carbon the carbon and other atoms/molecules/particles in the flame emit the light.

However, if the fuel for the flame is a carbon based compound, it will emit other oxidized carbon compounds (predominantly carbon monoxide and carbon dioxide). The oxidation process for carbon, hydrogen, sulfur, many metals has a net energy loss or emits energy (in otherwords the energy state of the products is lower then the energy state of the reactants). However, this is not always the most stable state as entropy dominate enthalpy and force a endothermic reaction. Think of the reactants as standing at an energy level of x, there is some ignition energy required to initiate the process, and the products then stand at some energy state below x. If the released energy has enough density and the reactants are present in sufficient concentrations, the released energy then initiates further reactions amongst the other reactants in a cascading effect. A retarding effect is the rate at which energy is absorbed by the fuel reactant to get the fuel into a vapor phase. So you are feeding the flame only as fast as the fuel source can decompose under heat to form a flammable vapor in the environment it exists.

Your right clarification is needed, I was targeting the 14 year old curiosity. The color of the flame, for a thermal source, is dependent on the temperature of the material emitting the light, where as the intensity of the light is determined by the emissivity of the material as well as the temperature. The color/wavelength/energy follows plank's law as depicted in wikipedia

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As the temperature increases the peak wavelength shifts to shorter wavelength and therefore higher energy. The vibration of the atom/molecule/particle is determined by the temperature but the amount of heat/light/phonons/photons/energy it can give off is determined by the energy it stores. In a wood fire the larger particle that are emitted into the plume are carbon pieces/particles/molecules and makeup the majority of the light emitted. This is why the flames from gas fireplaces are not as bright. The other way to view this is look at the gas lanterns, often used for camping. Without the mantle there is next to no light given off. The mantle acts as a converter of sorts, absorbing the heat generated and emitting light in the visible spectrum. The color of the flame is more often an indication of the temperature of the flame, majority of the chemical reactions do not generate photons in the visible spectrum but some do even without generating the heat.

By the way methane does contain carbon, it just burns converts to CO2 more efficiently.

How about this:

heat from combustion releases hot gases;

the hot gases are heated to a low plasma state;

the electron valences are elevated and then entropy occurs;

when the electrons drop to their lower state energy is conserved by the emission of photon pairs;

the color/wavelength of the photons/light is a result of the energy of this drop in valence;

15 years ago the science community didn't really understand the mechanics of flame or its propagation very well.

you may have to do a bit of research to understand all this, but with a little work/fun you can know more than most.

Hope this was of some help

Brad

you did not like my way of describing it then?

Your description was exact. I just tried to cut the elephant into bite size chunks.

I just put in some key words for further research. So yes I like it. I may have mist its posting do to my slow actions.

did you like mine?

Brad

> When trees are alive, their leaves take in energy from the sunlight and store some of this energy in the chemicals that make up the wood. Therefore, the wood is a fuel. One person (I think it was Steve Baer) described a fire as the unpeeling of this stored sunlight from the tree.

We were on the sea-shore today, and noticed that seashells also take up carbon from the atmosphere. Earth seems to have something about locking carbon below ground...

Okay John here we go...

One way burning is stopped is with a fire extinguisher. It is my understanding that when you spray a flame with a fire extinguisher you are taking away heat faster then it is being produced. Also, if I am correct most fire extinguishers spray CO^₂, so when you spray the fire with that you are removing oxygen from the fire (hence losing your oxidizer). Once that has occurred the flame has been extinguished temporarily (hence losing your ignition source). Then oxygen will surround the area again, but now there is nothing for the ignition. So when all is said and done you have lost one of your three things for a fire, which is your ignition.

Another is using sound-waves (I saw this one on "Mythbusters").

I do not know much about this. But what I do know is that you can out out small fires with sound. Because, if the wavelengths are correct, it creates pressure around the flame and forces it to go out. Making you, once again, lose your ignition source.

Hi Caleb

I have been playing with fire for nearly 40 years now. I started working on boilers that burned many tonnes of fuel every hour. Then I progressed to coal fired boilers that burned hundreds of tonnes of crushed coal every hour. The configuration of the flame could tell you a lot about how well the boiler was working. I am now working with the Bush Fire Brigade in Australia. In all that time nobody ever put the question about the flame in the way you did.

I keep three combustion text books within arms reach of my key board and none of them answered the question as well as it has been answered in this forum.

Engineers get paid to make things work and to come up with the right answers. The first step in that is to ask the right questions. Well done!

If you want to put out a fire with an extinguisher aim at the fuel not the flame. The flame is just an indication of the exothermic reaction going on.

Blue.

Caleb,

Your post shows some good thinking. When you say "losing your ignition source", do you mean the temperature of the fuel is too low for it to spontaneously ignite, or do you mean that the fuel has been removed (made unavailable)? I think you mean the first of these, which is correct for a CO₂ extinguisher (but not all types).

Carbon dioxide, CO₂, is stored at a high pressure in the extinguisher--notice that the tank is shaped with curves everywhere, no sharp edges or flat areas. When you discharge a CO₂ extinguisher, the gas is expanding to many times its stored volume. As it does so, the gas acts the same as the refrigerant gases in air conditioners, freezers, or refrigerators--it gets very cold. Q-1: Besides keeping the oxygen from reaching the fuel, what else do you think this very cold gas might be doing? If you look where you have just aimed the extinguisher, you often will see small (or even somewhat large) shapes of a white solid, which disappears after a while. Q-2: As you look at these piles of white solid you notice that no water runs away from them as they disappear, so what are they made of, if they are not frozen water?

A pressurized water extinguisher does the same things that a CO₂ extinguisher does. But it gets these same results of blocking the oxygen and cooling the fuel in a little bit different way. Q-3: Can you describe how it is doing these things?

A correction to your post---as you advance further in math and science, you will see that where the little "2" or other number (or even letters) go makes a big difference in the meaning. These different meanings are all by definition. You can put it above "²" which is the position used to label an isotope of a chemical, instead of below "₂" which is the position used to say how many of that atom you will find in that molecule. Thus, C¹⁴O¹⁷₂ is understood to be a little different than regular CO₂ (like the carbon atom is radioactive and those two oxygen atoms are very rare).

Here's an experiment for you to do. Things you need: a) some borax (sodium borate . . .) which is a white powder in a box you can find among the laundry or cleaning supplies in a grocery store, b) a teaspoon, c) a measuring cup, d) two similar sized small blocks or pieces of wood (not more than 2-in. or 5cm. in size). Here is the procedure: Dissolve a couple teaspoons of borax in a cup of water and soak one piece of dry wood in this for a few minutes. (If you are doing a real science experiment, you will be writing down each step with enough information, so you can repeat it exactly to see if the results are repeatable, or so you can repeat it with one part of it changed to see if the different results can tell you something new.) Then set this block of wood aside for a few days and let it dry. After it has dried completely (so it is just as dry as the other block), put them both in a fire and see how soon either one catches on fire and how well it burns. Before either block of wood is completely burned up, take them both out of the fire and set them on something that won't be damaged or burn, and see what happens to them. Q-4: Does the borax seem to be a fire retardant compound--why or why not?

Final question, then I'll let you go-- A dry chemical extinguisher sprays a powder on the fire, covering the fuel with it (if you sprayed at the base of the flames as was mentioned by another contributor). Q-5: Which of the fire extinguishing methods does a dry chemical extinguisher use?

For further education, ask your father or uncle to explain why a gasoline engine needs a spark plug to work but a diesel engine does not. This will tell you even more about fires and flames.

--John M.

Read through the posts back on this question - kudos to all for not 'flaming' the questioner. I noticed that everyone took the time to speak clearly and most on topic with references for additional information -

Was actually getting sort of tired hearing the bashing and gnashing of teeth about answering questions that could be 'search engined'.

Great work all.

Jim

I for one would like to hear form you again, Caleb. Just to know if what we rambled on about was helpful or not. Any more or further questions always welcome.

And the previous poster is right, you have chosen an excellent name.

Thank you for your time to answer my question guys.

Yes all your answers were helpful, I still have a couple posts to read, because there are so many. Also, My uncle and Father did say many of those things, it just seemed that they were unsure of what they were talking about.

By the way, I am homeschooled

Hey little menace,

I have found some things on flame colour on the web that might be of interest, if you already seen them or you already learnt it and done the tests, just let me know and I will "aim higher"

http://www.chemguide.co.uk/inorganic/group1/flametests.html

http://www.creative-chemistry.org.uk/activities/documents/flametests.pdf

http://www.creative-chemistry.org.uk/activities/flametests.htm

Have fun but remember, do not attempt any of these tests without supervision from an adult. Please promise I'll be in a lot of trouble if your house burns down and you blame me