Strain effects on the structure of counterflowing turbulent premixed flames

Mounaïm-Rousselle C., GÖKALP İ.

Symposium (International) on Combustion, cilt.25, sa.1, ss.1199-1205, 1994 (Scopus)

Özet

Dynamic and scalar structures of turbulent premixed flames stabilized in the opposed jet configuration are investigated. The opposed jet burner facility allows control of many parameters of turbulent premixed combustion, including the bulk and turbulent strain rates. The main mixture streams are enveloped in coflowing air to reduce flame bouncing, to render the turbulence structure more isotropic and homogeneous at the stagnation plane, and, therefore, to better match the major modelling assumptions. Detailed investigation of the velocity field confirms the strong variation of the initial turbulence parameters as the flow stagnates, and the similarity between nonreacting and reacting flow fields. It is clearly demonstrated that turbulent premixed flames stabilized in the opposed jet configuration are ideal for turbulent combustion model validation, as modification of the turbulence field by the flame is minimized. Two different extinction regimes of opposed jet turbulent premixed flames are identified. For small andmoderate burner separations, the total strain rate causes extinction. For large separation distaces, mixing and dilution by the external air are the causes of flame extinction. For the first regime, it is confirmed that bulk and turbulent strain rates should be taken into account simultaneously to establish the robustness of turbulent premixed flames. For the first time, the scalar structure of opposed jet turbulent premixed flames is explored by laserinducedrayleigh light-scattering technique. All the relevant parameters of instantaneous flame fronts are determined, and estimates of the flame surface density are proposed. It is shown that, for constant mixture composition and constant initial turbulence structure, the flame surface density increases with the bulk strain rate before its extinction value is closely approached. This result is discussed by using various ingredients of flamelet models. © 1994 Combustion Institute.