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Effect of Collar Length in Annular Counter-Flow Configuration on Extension of Turbulent Jet Diffusion Flame Blowout Limits
Sze Man Simon Chan, Shuichi Torii and Toshiaki Yano

Experiments are conducted to investigate the effects on jet diffusion flame blowout limits by positive height differences formed in an annular counterflow configuration. The differences are established by setting an outer cylinder above a fuel injection nozzle, with the cylinder stood concentrically around the nozzle. Results show that an increase in height differences alone triggers a vacuum pressure drop, which results in the limit extension and mitigation of flame lift-off propensity. These effects are augmented by an increase in air-suction flow rates. The formation of vacuum pressure acts concurrently to enhance these effects with shear flow control achieved by the air-suction and jet flows. A modified Thring-Newby parameter is proposed to elucidate the extension effect procured merely by the differences. A new supplementary explanation is imparted to accentuate the important effect of an increase in shear flow zone on mixing enhancement caused by an increase in height differences.

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