Effect of confinement on bluff-body burner recirculation zone characteristics and flame stability

Most practical burners have some form of confinement Confinement influences flame stability, emissions and heat transfer. Despite its importance in the design of industrial burners, no systematic and detailed fundamental study of flame confinement has been attempted. As a result, a data gap exists in an area important to burner design. To fill this data gap, we have performed a comprehensive test program that included several bluff-body burners, with different confinements and air jet sizes. This paper presents some of the velocity and fuel concentration data, obtained for four Blockage Ratios (BR). The velocity data were obtained by laser Doppler velocimetry and the concentration data were obtained by Raman imaging. The effect of confinement on velocity and concentration fields, and dame stability are analyzed. It is shown that, for the low BR case, recirculation zone characteristics and flame stability are unaffected by confinement. In contrast, confinement increases the recirculation zone size, distributes the fuel over a larger volume and enhances the stability of the high BR flames. To demonstrate a practical application of the data, concentration results are used to predict complex bluff-body flame regimes.