461-468.
Two-plane two-dimensional Rayleigh thermometry measurements have been carried out in turbulent premixed methane-helium-air flames in order to study the 3-D structure of the reaction zone. Three piloted premixed flames have been investigated at different Reynolds numbers near extinction. The instantaneous temperature, its mean profiles and rms fluctuations as well as the pdfs of the reaction zone thickness are presented in this paper. Also, the pdfs of the reaction zone location are presented. Helium has been added to the premixed jet in order to adjust the Rayleight cross-section of the fuel-air mixture to equal that of the surrounding air. This does not change the chemistry of the flame. The data in this paper show that the temperature, instantaneous, mean or rms, is reduced by stretch indicating significant chemical kinetic effects. Also, there is some evidence of extinguished parcels in the flame near extinction. On approaching extinction, the flame thickness increases and the deviation of reaction zone from its mean position is reduced. © 1992 Combustion Institute.