Vortex formation mechanism within fuel streams in laminar nonpremixed jet flames

Min Suk Cha*, Jinwoo Son, Sung Hwan Yoon, Hung Truyen Luong, Deanna A. Lacoste, Chae Hoon Sohn

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

7 Scopus citations


A vortical structure occurring at the fuel stream in laminar nonpremixed jet flames was recently found and shown to have both a fluid-dynamic impact on the flow field and a possible influence on the flame stability and soot formation. We designed a systematic experiment and numerical simulation to investigate the physical mechanisms of this recirculation phenomenon in a coflow system. We hypothesized that a negative buoyancy, caused by the fuel jet being heavier than the ambient air, may play a significant role in the recirculation. Therefore, we experimentally varied the density of the fuel jet using a binary mixture of methane and n-butane, and tested the density of the coflow oxidizer by replacing nitrogen with carbon dioxide. Several fuel jet velocities, flame temperatures, and nozzle diameters were also studied to thoroughly investigate all parameters that might possibly affect the recirculation. As a result, we found that our modified Richardson number, which is based on the cold density difference between the fuel and the coflow, the flame length, and the jet momentum flux, explained the physical mechanism of the recirculation well, with Ri ∼60 being the critical value for formation of the recirculation. The negative buoyancy was the primary driving force behind the recirculation, while the jet momentum mitigated its formation.

Original languageEnglish (US)
Pages (from-to)46-53
Number of pages8
JournalCombustion and Flame
StatePublished - Jan 2019


  • Negative buoyancy
  • Nonpremixed flame
  • Recirculation
  • Richardson number

ASJC Scopus subject areas

  • General Chemistry
  • General Chemical Engineering
  • Energy Engineering and Power Technology
  • Fuel Technology
  • General Physics and Astronomy


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