Influence of a bluff-body's shape on the stabilization regime of non-premixed flames

The objective of this experimental work is to perform an analysis of non-premixed flames' stabilization process by focusing on the geometry of the flame holder. Indeed, the effect of the bluff-body shape on the flame stabilization is of considerable interest to practical burner design. With this aim, a non-premixed flame is stabilized in a free flow. Two bluff-bodies are used whose geometry and aerodynamic characteristics are different: a disk shape, inducing a divergent flow and a tulip shape, allowing boundary layers development. Direct visualizations and an acrothermodynamic description of the isothermal and reacting flow are achieved. Results show the existence of various types of flames, according to the classical g-as jet to annular air flow velocity ratio, but the influence of the bluff-body shape on these stabilization regimes is also demonstrated. The tulip case promotes an enlargement of the stabilization domain and emphasizes a specific region "the laminar ring flame." On the contrary, due to strong reverse velocities, the stabilization process is modified in the wake of the disk. In conclusion, the present study points out that two parameters control the stabilization process of non-premixed flames: the gas jet to air velocity ratio and the bluff-body shape. They both have to be taken into account to improve the analysis. (C) 2001 by The Combustion Institute.