An Experimental Study of Flame Characteristics of Jet Diffusion Flames in Cylindrical Furnaces (2nd Report, Scaling of EINOx)

Abstract

The flame characteristics of confined flames are investigated for propane and hydrogen jet nonpremixed flames in cylindrical furnaces. The flame characteristics can be strongly dominated by the combination of the burner and furnace geometries. In the present study, the effects of the inner diameter of the cylindrical furnace D 1 , the turbulence at the flame boundary, and the global equivalence ratio φ are examined in terms of the emission of NOx. The emission index of NOx, EINOx, decreases roughly with these parameters. The decrease in EINOx is thought to be related to the dilution of mixtures by the burned gas and the flame stretch. The dilution is attributable to vortices formed at the bottom of the furnace, and the flame stretch is attributable to the air velocity difference ∆Ua created by two air nozzles. The EINOx characteristics are evaluated by the furnace Reynolds number Re,c based on the inner diameter of the furnace reflecting the dilution and the strain rate S∼Da-1 based on the air velocity difference, where Da indicates the Damköhler number. The EINOx is well characterized by the factor D 1 U F ∆Ua, which is proportional to Re,cDa-1. This result indicates that the confined nonpremixed flame is characterized by the furnace volume, not the flame volume, which is related to the reaction rate of the jet nonpremixed flame with coflowing air based on the flamelet model. This may imply that the furnace combustion should be modified from the flamelet concept owing to the dilution.

Effect of the distance between fuel and oxidizer nozzles on NOx emissions from spray combustion furnaces incorporating high-temperature preheated oxidizers

“…With regard to the relationship between NOx emissions and the recirculated burned gas, Noda and co-workers (Noda et al, 2007, Nada et al, 2008 investigated the effect of dilution resulting from burned gas recirculation on NOx emissions from laboratory-scale cylindrical furnaces with different diameters and found that a large furnace diameter enhances the extent of dilution. Noda's result suggests another cause for the reverse trend seen in the present study, in terms of the cross-sectional furnace size.…”