Flame (combustion

his article is about Flame luminous phenomenon that is produced by the incandescence of gases during combustion. For other uses of this term, see Flame (disambiguation) .

it is a luminous phenomenon that is produced by the incandescence of gases during combustion .

For the flame to start and be stable, the flame front must be stabilized. For this, the velocity of gas escapement and flame propagation must be coordinated with the input of oxidizer ( air ) and fuel . The flame front marks the separation between the burned gas and the unburned gas. This is where the main oxidation reactions take place. The thickness of the flame front can range from less than 1mm to fully occupy the combustion chamber. The spread of the flame is the movement of the flame through the gaseous mass. This propagation takes place at the flame front. If combustion is carried out with sufficient oxygen, Is complete. The flame produced in this case has little lighting power, which is why it is known by the name of oxidation flame or oxidant flame, and the excess of oxygen is high enough to oxidize metals . If oxygen is lacking, combustion is incomplete and the temperature reached is lower; in this flame the oxides of some metals are reduced ; the flame that is produced has a characteristic luminosity due to the incandescence of the coal that does not burn due to lack of oxygen. This flame is known by the name of reduction flame.



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  • 1 Structure of the flame
  • 2 Shape, color and temperature of the flame
  • 3 Classification of flames
  • 4 See Also
  • 5 Sources

Flame structure

Structure of the Flame

In non-luminous flames there are three clearly defined areas as shown in the figure:

  • Cold internal or internal zone, corresponds to gases that do not enter combustion, so its temperature is low.
  • Intermediate or reduction zone, is an intermediate mixture in which the combustion is incomplete and in which the metallic oxides are reduced. The reduction zone is generally limited to a mere envelope of the inner cone.
  • Outer or oxidation zone, which is the outermost part of the flame and surrounds the previous two; due to the abundance of oxygen there is complete combustion and the temperature is higher. The hottest point of the flame is inside this area.


Flame shape, color and temperature

The shape of a flame depends on the technical means that prepares the fuel / oxidizer; that is, it depends on the burner used, since it is in charge of spraying and distributing the fuel. If the combustion is good, the flame will not be opaque, blackish, … The unburned ones will give the black color. The temperature that the flame will reach will depend on:

  1. Composition and percentage of the oxidizer.
  2. Overall speed of combustion. This depends on:
  • Fuel reactivity.
  • Form and effectiveness of the combustion system.
  • Initial temperature of the reagents.

In current fluid fuel burners, the proportions of fuels and air are regulated to obtain flames of high calorific value. As a consequence of complete combustions, you would count the luminous flames that are produced in some burners by the influence of oxygen .


Flame classification

The flames are classified into 3 groups according to the parameters for a liquid fuel:

  1. Combustible fuel mixture.
  2. Fuel mixture speed.
  3. Position of the flame with respect to the burner mouth.
  4. Combustible fuel mixture.

1) Premix flame: The mixture of the two fluids is carried out partially or totally before reaching the combustion chamber.

2) Diffusion flame: (without pre-mixing) The fuel and the oxidizer mixes just at the moment of combustion.

  1. Fuel mixture speed.

1) Laminar: Mixing and transport phenomena occur at low temperatures.

2) Turbulent: The air / fuel mixture speeds are high. The vaporized mixture usually comes out whistling and whirling.

  1. Position of the flame with respect to the burner mouth.

1) Stationary flame: The fuel gradually burns as it passes through a certain part of the system. This is the ideal type of flame from an industrial point of view.

2) Free explosive flame: It is the one in motion.


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