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Diffusion flame

 
Diffusion Flame

 
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Diffusion flame
 
 
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- the interior of the flame contains unburnt fuel. This is opposite to combustion in a premixed flame
Premixed flame

A premixed flame is a flame in which the oxidizer has been mixed with the fuel before it reaches the flame front. This creates a thin flame front as all of the reactants are readily available....
. The fire breather's spurting of fuel (likely kerosene
Kerosene

Kerosene, sometimes spelled kerosine in scientific and industrial usage, also known as paraffin, is a combustible hydrocarbon liquid....
), combined with strong convection
Convection

Convection in the most general terms refers to the movement of molecules within fluids . Convection is one of the major modes of heat transfer and mass transfer....
 flows due to intense heat gives a turbulent diffusion flame.]]

In combustion
Combustion

Combustion or burning is a complex sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames, appearance of light flickering....
, a diffusion flame is a flame
Flame

A flame is the visible part of a fire. It is caused by a highly exothermic reaction taking place in a thin zone. If a fire is hot enough to ionize the gaseous components, it can become a Plasma ....
 in which the oxidizer combines with the fuel
Fuel

Fuel is any material that is burned or altered in order to obtain energy and to heat or to move an object. Fuel releases its energy either through a chemical reaction means, such as combustion, or nuclear means, such as nuclear fission or nuclear fusion....
 by diffusion
Diffusion

Molecular diffusion, often called simply diffusion, is a net transport of molecules from a region of higher concentration to one of lower concentration by random molecular motion....
. 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
Premixed flame

A premixed flame is a flame in which the oxidizer has been mixed with the fuel before it reaches the flame front. This creates a thin flame front as all of the reactants are readily available....
s because there may not be sufficient oxidizer for the reaction to go to completion, although there are some exceptions to the rule.






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- the interior of the flame contains unburnt fuel. This is opposite to combustion in a premixed flame
Premixed flame

A premixed flame is a flame in which the oxidizer has been mixed with the fuel before it reaches the flame front. This creates a thin flame front as all of the reactants are readily available....
. The fire breather's spurting of fuel (likely kerosene
Kerosene

Kerosene, sometimes spelled kerosine in scientific and industrial usage, also known as paraffin, is a combustible hydrocarbon liquid....
), combined with strong convection
Convection

Convection in the most general terms refers to the movement of molecules within fluids . Convection is one of the major modes of heat transfer and mass transfer....
 flows due to intense heat gives a turbulent diffusion flame.]]

In combustion
Combustion

Combustion or burning is a complex sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames, appearance of light flickering....
, a diffusion flame is a flame
Flame

A flame is the visible part of a fire. It is caused by a highly exothermic reaction taking place in a thin zone. If a fire is hot enough to ionize the gaseous components, it can become a Plasma ....
 in which the oxidizer combines with the fuel
Fuel

Fuel is any material that is burned or altered in order to obtain energy and to heat or to move an object. Fuel releases its energy either through a chemical reaction means, such as combustion, or nuclear means, such as nuclear fission or nuclear fusion....
 by diffusion
Diffusion

Molecular diffusion, often called simply diffusion, is a net transport of molecules from a region of higher concentration to one of lower concentration by random molecular motion....
. 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
Premixed flame

A premixed flame is a flame in which the oxidizer has been mixed with the fuel before it reaches the flame front. This creates a thin flame front as all of the reactants are readily available....
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.

The contexts for diffusion may vary somewhat. For instance a candle
Candle

A candle is a source of light, and sometimes a source of heat, consisting of a solid block of fuel and an embedded candle wick.Today, most candles are made from paraffin....
 uses the heat of the flame itself to vaporize its wax
Wax

Wax has traditionally referred to a substance that is secreted by bees and used by them in constructing their honeycombs.It is an imprecisely defined term generally understood to be a substance with properties similar to beeswax, namely...
 fuel and the oxidizer (oxygen
Oxygen

Oxygen no O2 produced; 2) O2 produced, but absorbed in oceans & seabed rock; 3) O2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer; 4-5) O2 sinks filled and the gas accumulates]]...
) diffuses into the flame from the surrounding air. While a gaslight
Gas lighting

Gas lighting refers to a technology used to produce lighting from a gaseous fuel including hydrogen, methane, carbon monoxide, propane, butane, or ethylene....
 flame (or the safety flame of a bunsen burner
Bunsen burner

A Bunsen burner is a common piece of laboratory equipment that produces a single open gas flame, which is used for heating, sterilization, and combustion....
) 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.

Diffusion flames have en entirey different appearent in in a microgravity environment. There is no convection to carry the hot combustion products away from the fuel source, which results 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.

See also

  • Premixed flame
    Premixed flame

    A premixed flame is a flame in which the oxidizer has been mixed with the fuel before it reaches the flame front. This creates a thin flame front as all of the reactants are readily available....


External links

  • , NASA
    NASA

    The National Aeronautics and Space Administration is an agency of the Federal government of the United States, responsible for the nation's public list of space agencies....