Diffusion flame

Encyclopedia : D : DI : DIF : Diffusion flame

In zero gravity, convection does not carry the hot combustion products away from the fuel source, resulting in a spherical flame front, such as this candle seen here.

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 flames because there may not be sufficient oxidizer for the reaction to go to completion, although this is not a rule. Diffusion flames tend to have a less-localized flame front than premixed flames.

The contexts for diffusion may vary. A candle uses evaporation to supply its wax fuel, and its oxidizer diffuses from the surroundings; a stove powered by natural gas may use a high-pressure jet of natural gas from a gas line.

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.

A nearly-turbulent diffusion flame.

See also

• Premixed flame

External links

• [Diffusion flames in microgravity], NASA
• [Diffusion and edge flames in opposed-jet burners]

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