The structure of nonpremixed hydrogen-air flames

An experimental and numerical study was performed to characterize the structure of diffusion flames stabilized in the mixing layer formed between counterflowing streams of hydrogen diluted with nitrogen and air diluted with nitrogen. Measurements were made with 15% to 30% hydrogen by volume in the fuel stream. The concentration of the reactants in the counterflowing streams as a function of their velocity at flame extinction was recorded over a wide parametric range. Using a UV Raman scattering system, the profiles of the mass fraction of the species H-2, O-2, H2O and N-2 and the temperature profiles were measured at two conditions, one close to and the other far from the critical conditions of extinction, Numerical calculations using detailed chemistry were performed to predict the flame structure and the results were found to agree well with the measurements. It is found that the chemical-kinetic mechanism employed here can accurately describe the combustion of hydrogen.