Turbulent flames with compositionally inhomogeneous inlets: Resolved measurements of scalar dissipation rates

Highly resolved measurements of scalar dissipation rates in turbulent piloted CH4/air flames with compositionally inhomogeneous inlets are presented. These were performed using Sandia's Raman–Rayleigh–LIF system but with data acquisition and processing strategies that result in enhanced spatial resolution and reduced noise. They complement earlier measurements with coarser resolution. The burner stabilising these flames enables variability in the mixture fraction profile at the exit plane. Earlier studies have shown enhanced stability at an optimal compositional inlet profile that leads to multiple modes of combustion, with premixed-stratified flames close to the jet exit but transitioning to diffusion-dominated burning downstream. It is found that at upstream locations, for jets with homogeneous inlets as well as for the high-temperature regions of flames with inhomogeneous inlets, both fine and coarse measurements of scalar dissipation rates yield similar results, giving confidence that measurements resolve the local dissipation scales. Downstream locations in homogeneous mixtures also show similar results for both coarse and fine measurements across all mixtures. Differences arise in the rich, inner regions of turbulent flames with inhomogeneous inlets, where the fine resolution measurements are more reliable due to the existence of steep gradients in composition. Both data sets provide a comprehensive platform to enhance the modelling of turbulent flames in the presence of multi-modes of combustion.