Rayleigh scattering measurements for molecular number Pt density in turbulent, premixed CH4-air flames are discussed, and Re data for both flamelet passage time distributions and power spectral density functions are reported and compared to the recent R n (r) predictions of Bray, Libby and Moss (1984). Measurement prob-ReΒ’)(_~, r) lems associated with variations in mixture-averaged Rayleigh rp, r R scattering cross section, index of refraction fluctuations, finite S n (f), S o ( f ) spatial and temporal resolution and with scattering from particles T are discussed. It is concluded that these effects are relatively ti minor in the reported experiments. Correction procedures are ?-m suggested for the effects of cross section variation and of finite [7 resolution, u' Passage time and spectral data support the Bray, Libby and X~ Moss hypothesis for the passage time distribution function,
x l , x 2 Furthermore, model predictions for the variation across the flame brush of mean passage times for both reactant and product eddies are in reasonable agreement with experiment. Finally, the data suggest that these mean times scale in part with Β’2 and 2 in the reactant flow.
List of symbols c = ( T -To)/(Too -To) E ~ (k, co) f f(c)
Gx ~ at hx, ht K m N (t), N (A t