Effects of fuel Lewis number on nitric oxide emission of diluted H 2 turbulent jet diffusion flames

Abstract

Results are reported on the effect of fuel Lewis number ( Le F ) in turbulent jet diffusion flames of diluted H 2 fuels. The results include the flame temperature, the emission index of nitric oxides (EINO x ), and the Damköhler number ( Da) scaling of EINO x ( EINO x /[ L f 3/d F 2U F] = Da n, where L f , d F , and U F are flame length, jet diameter, and jet exit velocity, respectively), which has been previously established. The effect of Le F was found to exist, although diminished in turbulent flames. Depending on the level and the type of dilution, the diluent that resulted in a lower value of Le F also had a higher flame temperature and produced larger values of both EINO x and the normalized emission index EINO x /[ L f 3 /d F 2 U F ], which is also considered as the global NO formation rate of the flame. The exponent n = −1/2 was reproduced for the present He-diluted flames whose Le F ≈ 1.0. For Ar- and CO 2-diluted flames with Le F ≥ 1.0 (20% and 40% dilution), n = −1/2 was also preserved. For dilution with 60% Ar or CO 2, whose Le F are 0.68 and 0.528, respectively, the exponent n was found to be positive. These results suggest the significant effects of Le F on NO x emission from turbulent diffusion flames.