NOx formation in hydrogen-methane turbulent diffusion flame under the moderate or intense low-oxygen dilution conditions

A numerical study of NOx emission in hydrogen-methane non-premixed flame has been conducted under the moderate or intense low-oxygen dilution (MILD) conditions. In the simulation, the Eddy Dissipation Concept (EDC) model is applied. The predictions are validated by the experimental results for the three flames with the oxygen mass fraction varying from 3% to 9%. The model with the detailed chemical mechanisms can succeed in capturing the trend lines of NO level and predicting the NO formation at the low oxygen level. The simulation indicates that the low oxygen level leads to suppression of the NO formation. Analysis of the NO formation mechanisms shows that the NNH and prompt routes play a significant role in the NO formation under the MILD conditions. The effects of the coflow air temperature and hydrogen concentration in the fuel mixture on the NO formation are taken into account in the study. The results demonstrate that a decrease in fuel hydrogen concentration or a low coflow air temperature contributes to suppression of the NO formation.