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Non-premixed Flames (Diffusion Flames)

  • Sara McAllister
  • Jyh-Yuan Chen
  • A. Carlos Fernandez-Pello
Chapter
Part of the Mechanical Engineering Series book series (MES)

Abstract

In many combustion processes, the fuel and oxidizer are separated before entering the reaction zone where they mix and burn. The combustion reactions in such cases are called “non-premixed flames,” or traditionally, “diffusion flames” because the transport of fuel and oxidizer into the reaction zone occurs primarily by diffusion. Many combustors operate in the non-premixed burning mode, often for safety reasons. Since the fuel and oxidizer are not premixed, the risk of sudden combustion (explosion) is eliminated. Chemical reactions between fuel and oxidizer occur only at the molecular level, so “mixing” between fuel and oxidizer must take place before combustion. In non-premixed combustion the fuel and oxidizer are transported independently to the reaction zone, by convection and diffusion, where mixing of the fuel and oxidizer occurs prior to their reaction. Often the chemical reactions are fast, hence the burning rate is limited by the transport and mixing process rather than by the chemical kinetics. Consequently, greater flame stability can be maintained. This stable characteristic makes diffusion flames attractive for many applications, notably aircraft gas-turbine engines. Topics covered in this chapter include: (1) a detailed description of a candle flame, (2) the structure of non-premixed laminar jet flames, (3) theoretical and empirical expressions for laminar jet flame height, (4) Burke-Schumann jet diffusion flames, (5) turbulent jet flames including liftoff height and blowout limit, and (6) a short discussion of condensed fuel fires.

Keywords

Volumetric Flow Rate Diffusion Flame Premix Flame Flame Surface Fuel Vapor 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

References

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    Hottel HC, Hawthorne WR (1949) Diffusion in laminar jet flames. Symposium on Combustion and Flame, and Explosion Phenomena 3(1):254–266.CrossRefGoogle Scholar
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    Lee KO, Megaridis CM, Zelepouga S, Saveliev AV, Kennedy LA, Charon O, Ammouri F (2000) Soot formation effects of oxygen concentration in the oxidizer stream of laminar coannular nonpremixed methane/air flames. Combustion and Flame 121:322–333.Google Scholar
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    Smyth KC, Miller JH, Dorfman RC, Mallard WG, Santoro RJ (1985) Soot inception in a methane/air diffusion flame as characterized by detailed species profiles. Combustion and Flame 62(2):157–181.CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media, LLC 2011

Authors and Affiliations

  • Sara McAllister
    • 1
  • Jyh-Yuan Chen
    • 1
  • A. Carlos Fernandez-Pello
    • 1
  1. 1.Department of Mechanical EngineeringUniversity of California, BerkeleyBerkeleyUSA

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