Evaluation of partially premixed turbulent flame stability from mixture fraction statistics in a slot burner

ABSTRACT

Partially premixed combustion is characterized by mixture fraction inhomogeneity upstream of the reaction zone and occurs in many applied combustion systems. The temporal and spatial fluctuations of the mixture fraction have tremendous impact on the combustion characteristics, emission formation, and flame stability. In this study, turbulent partially premixed flames are experimentally studied in a slot burner configuration. The local temperature and gas composition is determined by means of one-dimensional, simultaneous detection of Rayleigh and Raman scattering. The statistics of the mixture fraction are utilized to characterize the impact of the Reynolds number, the global equivalence ratio, the progress of mixing within the flame, as well as the mixing length on the mixing field. Furthermore, these effects are evaluated by means of a regime diagram for partially premixed flames. In this study, it is shown that the increase of the mixing length results in a significantly more stable flame. The impact of the Reynolds number on flame stability is found to be minor.

KEYWORDS:

• Partially premixed flame
• flame stability
• turbulent combustion
• line-Raman measurement
• Rayleigh measurements
• turbulent slot burner

Acknowledgments

This work was performed within the Cluster of Excellence “Tailor-Made Fuels from Biomass,” which is funded by the Excellence Initiative of the German federal state governments to promote science and research at German universities. The support of the design office and workshop of the Institute for Combustion Technology in the burner development and setup are gratefully acknowledged.