The Effect of Upstream Annular Cavities in Circular Jet Burners on Stability Characteristics of Jet Diffusion Flames

Abstract

The characteristics of diffusion flames from circular jet burners in the presence of upstream annular cavities are investigated experimentally. The influences of cavity dimensions such as cavity diameter and cavity length, and postcavity length, on methane flame characteristics are investigated. Experimental investigation employing 18 circular jet burners with an upstream cavity of different dimensions and a burner without cavity has been carried out. For burners with cavity, smaller flame lengths are obtained in the laminar region when compared to the burner without cavity due to enhanced mixing. The transition from laminar to turbulent regime occurs at higher flow rates for burners with cavity. Liftoff velocity, the fuel velocity at which the flame lifts off from the burner exit, and blowoff velocity, at which the flame blows off, are higher with the inclusion of cavity. This suggests that improved flame stability and increased operating range can be attained in burners with cavity as compared to that without cavity. Within the burners with cavity, there is an optimum cavity diameter and postcavity length, which provides maximum flame stability. The cavity length to diameter ratio is also a critical parameter; when the ratio is less than unity, increased stability is achieved.

Keywords:

• Annular cavity
• Blowoff velocity
• Diffusion flames
• Flame stability
• Lifted flame
• Liftoff height

Notes

Note. Cavity dimension = 8 mm; L₁ = 10 mm; L₂ = 6 mm.