Comparative flame structure investigation of normal and inverse turbulent non-premixed oxy-fuel flames using experimentally recorded and numerically predicted Rayleigh and OH-PLIF signals

The structure and characteristics of a turbulent inverse and normal oxy-fuel diffusion flame are investigated. Previous investigations reported in the literature looked at flame characteristics of laminar inverse diffusion flames and their differences to normal diffusion flames. Only few investigations are reported for turbulent inverse diffusion flames and they did not compare the results to the corresponding normal configuration.The present study uses a combined experimental and numerical approach to compare and analyze a turbulent non-premixed inverse oxy-fuel and a corresponding normal flame, both are non-piloted. Measurements were conducted using simultaneously recorded planar Rayleigh scattering and OH-LIF signals. Due to the significant variation of the effective Rayleigh cross section in mixture fraction space and the unknown OH quenching contributions, a comparison of derived quantities such as temperature and OH mole fraction is not possible. Therefore, the Rayleigh and OH-LIF signals were incorporated in the LES flamelet/progress variable approach used here. This allows for a direct comparison of experimentally recorded and numerically predicted Rayleigh and OH-PLIF signals for the flame structure analysis, which includes the joint PDF of both quantities. The two flames are compared in terms of the local flame structure. In addition, differences in the mixing field and especially in the location of turbulent/non-turbulent interface are investigated.