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

Abstract

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 (χr) and 3D (χ) scalar dissipation increases with axial distance along the flame such that the ratio χ/χr 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.