Flame: Difference between revisions
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Generally speaking, the coolest part of the flame will be red, transitioning to orange, yellow and white as the temperature increases as a result of changes in blackbody radiation. For a given flame's region, the closer to white on this scale, the hotter that section of the flame is. A blue-colored flame emerges when the amount of soot decreases and the blue emissions from molecules become dominant. |
Generally speaking, the coolest part of the flame will be red, transitioning to orange, yellow and white as the temperature increases as a result of changes in blackbody radiation. For a given flame's region, the closer to white on this scale, the hotter that section of the flame is. A blue-colored flame emerges when the amount of soot decreases and the blue emissions from molecules become dominant. |
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The common distribution of a flame under normal gravity conditions depends on convection, as soot tends to rise to the top of a flame (such as in a candle in normal gravity conditions) making it yellow. In [[microgravity]] or [[zero gravity]], such as an [[outer space]] environment, convection no longer occurs and the flame becomes spherical, with a tendency to become bluer and more efficient. |
The common distribution of a flame under normal gravity conditions depends on convection, as soot tends to rise to the top of a flame (such as in a candle in normal gravity conditions) making it yellow. In [[microgravity]] or [[zero gravity]], such as an [[outer space]] environment, convection no longer occurs and the flame becomes spherical, with a tendency to become bluer and more efficient. Tere are several possible explanations for this difference, of which the most likely is the hypothesis that the temperature is sufficiently evenly distributed that soot is not formed and complete combustion occurs. <ref> [http://microgravity.grc.nasa.gov/combustion/cfm/usml-1_results.htm CFM-1 experiment results], National Aeronautics and Space Administration, April 2005.</ref> Experiments by NASA in microgravity reveal that [[diffusion flame]]s in microgravity allow more soot to be completely oxidised after they are produced than do diffusion flames on Earth, because of a series of mechanisms that behave differently in microgravity when compared to normal gravity conditions. <ref>[http://microgravity.grc.nasa.gov/combustion/lsp/lsp1_results.htm LSP-1 experiment results], National Aeronautics and Space Administration, April 2005.</ref> [[Premixed flame]]s in microgravity burn at a much slower rate and more efficiently than even a candle on Earth, and last much longer. <ref>[http://microgravity.grc.nasa.gov/combustion/lsp/lsp1_results.htm SOFBAL-2 experiment results], National Aeronautics and Space Administration, April 2005.</ref> These discoveries have potential applications in [[applied science]] and [[industry]], especially concerning [[fuel efficiency]]. |
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==References== |
==References== |
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Revision as of 01:13, 25 April 2006
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Flame is a plasma, an ionised gaseous product of combustion, and an exothermic self-sustaining oxidation reaction. In layman's terms, a flame could be said to be, for example, the visible part of a fire.
The color and temperature of the flame are dependent on the type of fuel involved in the combustion. Let's say you hold a lighter to a candle. This applied heat causes the fuel molecules to evaporate. They then react with oxygen, giving off enough heat to sustain a consistent flame. The resulting increases in temperature tears apart some of the fuel molecules, forming various incomplete combustion products and free radicals. Sufficient energy in the flame will excite the electrons in these products, which results in the emission of visible light. As the combustion temperature increases, so does the energy of the electromagnetic radiation given off by the flame. This is why the hottest visible flame is in the blue/violet region of the visible spectrum.
Other oxidizers besides oxygen can be used. Hydrogen burning in chlorine produces a flame as well, producing gaseous hydrogen chloride (HCl). Other possible combinations are fluorine and hydrogen or hydrazine and nitrogen tetroxide.
There are different methods of distributing the required components of combustion to a flame. In a diffusion flame, oxygen and fuel diffuse into each other; where they meet the flame occurs. In a premixed flame, the oxygen and fuel are premixed beforehand, which results in a different type of flame. Candle flames operate through evaporation of the fuel.
Flame colors
[dubious ]
Flame color depends on three components, blackbody radiation, spectral line emission, and to a lesser degree spectral line absorption. Depending on oxygen supply, which determines the rate of combustion, temperature and reaction paths, different color hues can be observed in flames. Recent discoveries by the National Aeronautics and Space Administration (NASA) of the United States also have found that gravity plays a role. [1] Pictured on the right is a Bunsen burner burning mainly methane.
In a laboratory under normal gravity conditions and with a closed oxygen valve, a Bunsen burner burns with yellow flame (also called a safety flame) at 1,000°C. With increasing oxygen supply less blackbody-radiating soot is produced, and the combustion reaction creates enough energy to ionize gas molecules in the flame, leading to a blue appearance.
Flame temperatures of common items include a blowlamp at 1,300°C, a candle at 1,400°C, or a much hotter oxy-acetylene combustion at 3,000°C.
Generally speaking, the coolest part of the flame will be red, transitioning to orange, yellow and white as the temperature increases as a result of changes in blackbody radiation. For a given flame's region, the closer to white on this scale, the hotter that section of the flame is. A blue-colored flame emerges when the amount of soot decreases and the blue emissions from molecules become dominant.
The common distribution of a flame under normal gravity conditions depends on convection, as soot tends to rise to the top of a flame (such as in a candle in normal gravity conditions) making it yellow. In microgravity or zero gravity, such as an outer space environment, convection no longer occurs and the flame becomes spherical, with a tendency to become bluer and more efficient. Tere are several possible explanations for this difference, of which the most likely is the hypothesis that the temperature is sufficiently evenly distributed that soot is not formed and complete combustion occurs. [2] Experiments by NASA in microgravity reveal that diffusion flames in microgravity allow more soot to be completely oxidised after they are produced than do diffusion flames on Earth, because of a series of mechanisms that behave differently in microgravity when compared to normal gravity conditions. [3] Premixed flames in microgravity burn at a much slower rate and more efficiently than even a candle on Earth, and last much longer. [4] These discoveries have potential applications in applied science and industry, especially concerning fuel efficiency.
References
- ^ Spiral flames in microgravity, National Aeronautics and Space Administration, 2000.
- ^ CFM-1 experiment results, National Aeronautics and Space Administration, April 2005.
- ^ LSP-1 experiment results, National Aeronautics and Space Administration, April 2005.
- ^ SOFBAL-2 experiment results, National Aeronautics and Space Administration, April 2005.