TY - CONF

T1 - Lifted reaction zones in premixed turbulent bluff-body stabilized flames

AU - Most, Dieter

AU - Dinkelacker, Friedrich

AU - Leipertz, Alfred

N1 - Funding Information: The authors gratefully acknowledge financial support for parts of the work by the Deutsche Forschungsgemein-schaft.

PY - 2002

Y1 - 2002

N2 - Flame lift-off phenomena are well known in turbulent non-premixed flames but less investigated in turbulent premixed flames. In the special case of flames stabilized by the re-circulation of burnt gases a particular type of lifted reaction zone can be observed, which is not only originated simply by the lack of heat, but by some other mechanisms, e.g., ignition delay. In principle this premixed flame lift-off might be based either on turbulent effects. To investigate these lift-off mechanisms, experiments were conducted at bluff body stabilized premixed-CH4 air flames, where flow and flame parameters were varied systematically over a broad range of exit velocities and stoichiometries. While the lift-off height was measured with laser-induced OH fluorescence, also the local characteristic turbulent flow and temperature field was measured to allow correlated data determination for the lift-off height. Three different theoretical model approaches were elucidated for the prediction of this lifted reaction zones by comparing local flow, turbulence, and reaction parameters with the local "burning" or "non-burning" status. Two different lift off criteria had to be met for this burner configuration. For very lean mixtures, the chemical dominated ignition delay was the rate-determining step. For other cases the lift-off height could be determined by a newly described turbulent mixing dominated model. In contrast to this, a dimensionless turbulent strain rate, often described with a Kovasznay or Karlovitz number, was not a suitable criterion. Original is an abstract.

AB - Flame lift-off phenomena are well known in turbulent non-premixed flames but less investigated in turbulent premixed flames. In the special case of flames stabilized by the re-circulation of burnt gases a particular type of lifted reaction zone can be observed, which is not only originated simply by the lack of heat, but by some other mechanisms, e.g., ignition delay. In principle this premixed flame lift-off might be based either on turbulent effects. To investigate these lift-off mechanisms, experiments were conducted at bluff body stabilized premixed-CH4 air flames, where flow and flame parameters were varied systematically over a broad range of exit velocities and stoichiometries. While the lift-off height was measured with laser-induced OH fluorescence, also the local characteristic turbulent flow and temperature field was measured to allow correlated data determination for the lift-off height. Three different theoretical model approaches were elucidated for the prediction of this lifted reaction zones by comparing local flow, turbulence, and reaction parameters with the local "burning" or "non-burning" status. Two different lift off criteria had to be met for this burner configuration. For very lean mixtures, the chemical dominated ignition delay was the rate-determining step. For other cases the lift-off height could be determined by a newly described turbulent mixing dominated model. In contrast to this, a dimensionless turbulent strain rate, often described with a Kovasznay or Karlovitz number, was not a suitable criterion. Original is an abstract.

UR - http://www.scopus.com/inward/record.url?scp=0036927334&partnerID=8YFLogxK

M3 - Paper

SP - 31

T2 - 29th International Symposium on Combustion

Y2 - 21 July 2002 through 26 July 2002

ER -