The mixing field and flame structure near the reaction zone of turbulent planar flames at different levels of mixture inhomogeneity

Turbulent flames with compositionally inhomogeneous mixtures are commonly used in many combustion systems. In this work, turbulent planar jet flames issued from a concentric flow slot burner, CFSB, were used to study the impact of mixture inhomogeneity near the flame sheet. The CFSB burner can control the mixing inhomogeneity by changing the mixing length "L" between the concentric fuel and air slot nozzles. At various levels of mixture inhomogeneity, the mixing field, presented by mixture fraction, Z, distribution, and the flame structure was investigated via simultaneous Rayleigh and OH-PLIF imaging technique. Our previous study investigated the mixing field immediately downstream of the burner exit in non-reacting conditions. The PDFs of Z showed that the mixing field covered a wide range of mixture fractions, where the high flame stabilization occurred when a large portion of the PDF(Z) was located within the fuel flammability limits. This work showed that further downstream, the highly stabilized flames were also obtained when the range of fluctuations in the mixture fraction was close to the stoichiometric mixture fraction. Moreover, plotting the mixing field using the scatter plot within the mixing regime diagram for various flame conditions showed that the mixing field downstream of the burner exit consistently follows the mixing diagram classification. Moreover, a close inspection of the flame structure showed that the flame sheet varies from thick, and corrugated at a low and high levels of mixing to thin flame sheet but less corrugated and that at a particular mixing normalized length L/D = 7. The flame corrugation data showed that the flame stability occurs at a minimum corrugation factor.