Diffusion flame
3882239
126465563
2007-04-27T20:02:47Z
Guyinblack25
1340380
Corrected wikilink
[[Image:Candleburning.jpg|thumb|right|The common flame of a [[candle]] is a classic example of a diffusion flame. Its yellow color owing to the large amount of [[incandescent]] soot particles in the incomplete combustion reaction of the flame.]]
In [[combustion]], a '''diffusion flame''' is a [[flame]] in which the [[oxidizer]] combines with the [[fuel]] by [[diffusion]]. As a result, the flame speed is limited by the rate of diffusion. Diffusion flames tend to burn slower and to produce more soot than [[premixed flame]]s because there may not be sufficient oxidizer for the reaction to go to completion, although there are some exceptions to the rule. The soot typically produced in a diffusion flame becomes [[incandescent]] from the heat of the flame and lends the flame its readily identifiable orange-yellow color. Diffusion flames tend to have a less-localized flame front than premixed flames.
[[Image:Candlespace.jpg|thumb|left|In [[Weightlessness|zero gravity]], convection does not carry the hot combustion products away from the fuel source, resulting in a spherical flame front, such as in the candle seen here. This is a rare example of a diffusion flame which does not produce much soot and does not therefore have a typical yellow flame.]]
The contexts for diffusion may vary somewhat. For instance a [[candle]] uses the heat of the flame itself to [[vaporize]] its [[wax]] fuel and the oxidizer ([[oxygen]]) diffuses into the flame from the surrounding air. While a [[Gas lighting|gaslight]] flame (or the safety flame of a [[bunsen burner]]) uses fuel already in the form of a vapor.
Diffusion flames are often studied in counter flow (also called opposed jet) burners. Their interest is due to possible application in the flamelet model for turbulent combustion. Furthermore they provide a convenient way to examine strained flames and flames with holes. These are also known under the name of "edge flames", characterized by a local extinction on their axis because of the high strain rates in the vicinity of the stagnation point.
[[Image:Australia_Cairns_Flame.jpg|thumb|A nearly-[[turbulent]] diffusion flame.]]
==See also==
* [[Premixed flame]]
==External links==
*[http://microgravity.grc.nasa.gov/combustion/lsp/lsp_overview.htm Diffusion flames in microgravity], [[NASA]]
*[http://www.andreaciani.net/research.htm Diffusion and edge flames in opposed-jet burners]
[[Category:Fire]]
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