Extreme role of preferential diffusion in turbulent flame propagation

Sheng Yang, Abhishek Saha, Wenkai Liang, Fujia Wu, Chung K. Law

Research output: Contribution to journalArticlepeer-review

46 Scopus citations


In this paper we demonstrate the essential role of molecular diffusion in the structure and propagation of turbulent flames. We first show that mixtures whose concentrations are near or beyond the conventional flammability limits can be rendered to burn strongly in turbulence, provided the controlling molecular mass diffusivity of the mixture exceeds its thermal diffusivity, namely the mixture Lewis number (Le) is less than unity. The associated turbulent flame speeds in such cases can be orders of magnitude greater than the corresponding laminar flame speeds, with distinctive finger-shape structures on the flame surfaces. Furthermore, this facilitation effect is completely flipped for Le > 1 mixtures, leading to actual weakening of the nominally enhancing effect of turbulence on their burning intensity. Mechanistically, such opposite effects are consequences of the coupling between preferential diffusion and the wrinkled laminar flamelets constituting the turbulent flame structure.

Original languageEnglish (US)
Pages (from-to)498-504
Number of pages7
JournalCombustion and Flame
StatePublished - Feb 2018

All Science Journal Classification (ASJC) codes

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


  • Flammability limit
  • Preferential diffusion
  • Turbulent flame


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