Diffusion flame

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Different flame types depending on the amount of air that passes through the air valve:
1 valve closed (diffusion flame)
2 valve half open
3 valve almost completely open
4 valve fully open (premixed flame)

The diffusion flame is the flame of a Bunsen burner that burns without air premixing. The oxygen required for combustion diffuses - like all other air components - over the edge of the flame into the flame, which is why it is increasingly poorly supplied with oxygen towards its core. In the core, therefore, the fuel only partially burns.

Laminar diffusion flames are only used as a pilot flame in technology and as a candle flame in everyday life because of the high unburned content, which can be recognized by the strong soot in the flames . Earlier oil stoves also worked on this principle; however, this is technically out of date.

Turbulent diffusion flames continue to play an important role in energy technology, mainly in the technical combustion of solid and liquid fuels, for example in diesel engines or gasoline engines with direct injection.

Sub-areas

The diffusion flame can be divided into three sub-areas:

  • A cold area at the beginning of the combustion path, i.e. H. in the immediate vicinity of the gas or oil leak. In this area there is no reaction worth mentioning , the flame core consists of unburned gas or oil.
  • The second area is called luminous , in it the carbon split off from the hydrocarbon by the heat of the flame edge glows with a yellow color. Therefore one speaks of a yellow flame.
  • The third area is the outer, hot edge of the flame, in which the exothermic combustion reaction to carbon dioxide and water vapor takes place.

For the cause of the different colors of these flames, see flame characterization .

Premix flame

The opposite of a diffusion flame is also known as a premix flame. The oxygen is mixed into the fuel beforehand, which means that the combustion can proceed more completely and thus hotter. In addition, there is a significant increase in the development of noise (rustling flame). Intermediate types of the diffusion flame and the premix flame are called partial premix flames.

Individual evidence

  1. ^ Gisbert Rodewald: fire theory . W. Kohlhammer Verlag, 2006, ISBN 978-3-17-019129-7 , pp. 231 ( limited preview in Google Book search).
  2. ↑ a b c Joachim Georg Wünning: Manual of burner technology for industrial furnaces, basics, burner techniques, applications . Vulkan-Verlag GmbH, 2007, ISBN 978-3-8027-2938-6 , p. 53 ( limited preview in Google Book search).
  3. ↑ Günter P. Merker, Rüdiger Teichmann: Fundamentals of internal combustion engines, functionality, simulation, measurement technology . Springer-Verlag, 2014, ISBN 978-3-658-03195-4 , pp. 158 ( limited preview in Google Book search).
  4. ^ Günter P. Merker, Christian Schwarz, Gunnar Stiesch, Frank Otto: Combustion engines simulation of combustion and pollutant formation . Springer-Verlag, 2013, ISBN 978-3-322-96774-9 , pp. 388 ( limited preview in Google Book search).
  5. ↑ a b Bruno P. Kremer, Horst Bannwarth: Introduction to Laboratory Practice, Basic Competencies for Laboratory Newbies . Springer-Verlag, 2014, ISBN 978-3-642-54334-0 , pp. 101 ( limited preview in Google Book search).
  6. ↑ Ralf Geiß: The transformation of substances From phenomena to theory . 2015, p. 2–64 ( limited preview in Google Book Search).