Hydroxyl and Rayleigh scattering time-series measurements in turbulent non-premixed H₂/CH₄/N₂-air jet flames

Hydroxyl laser-induced fluorescence and laser Rayleigh scattering time-series measurements were obtained for a set of five turbulent non-premixed H₂/CH₄/N₂-air jet flames in the range 13,100 < Re < 21,000. For each of the flames, high-repetition rate time-series measurements were made at various axial locations between x/D = 20 and x/D = 40. The autocorrelation functions were self-similar for both the [OH] and LRS measurements, and could be fully characterized by their integral time scales. Integral time scales were computed along the centerline at various axial heights. The density and [OH] time scales portrayed an increase with distance downstream, but the density time scales are always greater than those for [OH] by a factor of two to four. At a fixed peak radial temperature location, the OH integral time scales decreased with increasing Reynolds number as Re^-1.41. The density time scales showed a similar trend of Re^1.42. Along the jet centerline, for a given Re, the ratio of density to OH integral time scale was largely invariant. However, this ratio rose with increasing Re, suggesting an enhanced reduction in the [OH] time scale owing to more discernable fluctuations of the thin [OH] layer as compared to the wider density layer. Measured [OH] and density time scales were also compared to predicted time scales using mixture fraction simulations. This is an abstract of a paper presented at the 30th International Symposium on combustion (Chicago, IL 7/25-30/2004).