A transition on minimum ignition energy for lean turbulent methane combustion in flamelet and distributed regimes

C. C. Huang, S. S. Shy, C. C. Liu, Y. Y. Yan

Research output: Contribution to journalConference articlepeer-review

82 Scopus citations

Abstract

Minimum ignition energy (MIE) of lean methane-air mixtures is quantitatively measured using a high-power pulse generator which can vary ignition energies of a spark-electrode in the central position of a large fan-stirred cruciform burner. The burner equipped with a pair of counter-rotating fans and perforated plates can be used to generate isotropic turbulence having a very wide range of turbulent intensities (u′) up to 8 m/s with negligible mean velocities. Observations of ignition, flame kernel development, and subsequent flame propagation in the central uniform region of the burner are recorded by a CMOS high-speed camera (5000 frames/s), showing distributed-like flames of very dispersive and fragmental structures with filiform edges for the first time. A complete MIE data set of lean methane-air mixtures at the equivalence ratio φ = 0.6 as a function of u′/S L is obtained, where SL is the laminar burning velocity. It is found that there is a transition on values of MIE due to different modes of combustion. Before the transition, MIE only increases gradually with u′/SL. Across the transition when u′/SL > 24 corresponding to the commonly defined turbulent Karlovitz number Ka = (u′/SL)2(ReT)-0.5 > 8, MIE increases abruptly, where ReT is the turbulent Reynolds number based on the integral length scale of turbulence. This transitional value of Ka is much greater than the Klimov-Williams criterion (Ka = 1). Since values of MIE under different levels of turbulence should be relevant to the size of the reaction zone at least in the beginning of turbulent combustion, MIE ∼ δ3 based on an order-of-magnitude criterion where δ is the reaction zone thickness. It is thus concluded that this new experimental finding proves the existence of both thin and broken reaction zones regimes proposed by Peters for a new regime diagram of premixed turbulent combustion.

Original languageEnglish
Pages (from-to)1401-1409
Number of pages9
JournalProceedings of the Combustion Institute
Volume31 I
Issue number1
DOIs
StatePublished - 2007
Event31st International Symposium on Combustion - Heidelberg, Germany
Duration: 5 Aug 200611 Aug 2006

Keywords

  • Flamelet and distributed regimes
  • Lean premixed turbulent methane combustion
  • Minimum ignition energy
  • Thin and broken reaction zones
  • Transition

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