On the joint statistics of mixture fraction and reaction progress variable in mixed modes of combustion

This paper presents joint statistics of mixture fraction and an oxygen-based reaction progress variable in turbulent piloted flames of methane with compositionally inhomogeneous inlets. Previous studies of these flames have shown that inhomogeneity at the exit plane increases flame stability which has been attributed to premixed-stratified combustion occurring close to the jet exit. It is confirmed that for these partially premixed cases, through joint statistics and conditional probabilities, flammable mixtures close in the pilot-jet mixing layer are significantly more likely than in an equivalent homogeneous flame. This increased probability of high progress variable samples reinforces previous theories of upstream heat release supporting global flame stability in jets with inhomogeneous inlets. The correlation between mixture fraction and the reaction, which is an important parameter in the modeling of mixed-mode combustion is also discussed. This correlation also change with the introduction of compositional inhomogeneity.