The effects of N2 and steam dilution on NO emission for a H2/Air micromix flame

Abstract

The different effects of N2 and water steam dilution on the NO emission from a micromix H2/air flame were experimentally and numerically studied. NO emission was measured using Fourier transform infrared spectroscopy gas analyzer (FTIR). Numerical simulation of the H2/air flame was carried out with realizable k-ε model and the Eddy Dissipation Concept (EDC) model. Two pseudo species were introduced in the simulations to numerically isolate the thermal-dilution, direct chemical and third-body effect of the steam. The experimental and numerical results show that NO emission with steam dilution is about 20%∼50% of the emission with N2 dilution at the same equivalence ratio (φ) and dilution ratio (D). The present simulation results show that the thermal-dilution and direct chemical effects of steam account for 50.8%∼92.1% and 5.8%∼15.8% of the total NO emission, respectively, while the third-body effect of steam shows less impact on NO emission. Specifically, the third-body effect slightly promotes the formation of H and NO at lower φ (0.6–0.8) and suppresses the formation of H and NO at higher φ (0.9–1.0) through inhibiting the third-body reaction of H + O2 + M ⇔ HO2 + M. In addition, the direct chemical and third-body effects of steam always decrease the formation of NO from the NNH route.