Statistics of scalar dissipation and reaction progress in turbulent flames with compositional inhomogeneities

This paper presents detailed measurements of three-dimensional (3D) scalar dissipation rates collected in turbulent, piloted flames with varying degree of compositional inhomogeneity. Joints statistics of mixture fraction and reaction progress variable are also shown for a range of conditions. These measurements complement the already existing substantial data set for mixed-mode flames stabilized on the Sydney piloted burner with compositionally inhomogeneous inlets. It is found that the difference between 2D (χ_r) and 3D (χ) scalar dissipation increases with axial distance along the flame such that the ratio χ/χ_r may be as high as 2.6. The effects of spatial resolution become more significant as compositional inhomogeneity increases. Mixture fraction, ξ is well-correlated with reaction progress variable, c, in turbulent homogenous flames but the correlations deteriorates significantly as the compositional inhomogeneity increases. This transition should clearly be accounted for in modeling mixed-mode combustion. A new mode of conditioning the scalar dissipation data with respect to burnt and unburnt fluid samples reveal separate trends: while the levels of χ remain similar for burnt samples, unburnt fluid experiences increasing levels of χ as the flames approach blow-off.