Influence of buoyancy on the mixing, flame structure, and production of NO in hydrogen diffusion flames

This study investigates the impact of buoyancy on the mixing and flame structure of hydrogen jet diffusion flames. A validated Computational Fluid Dynamics (CFD) model for hydrogen diffusion flames is developed, employing the k-w turbulence model and a steady flamelet combustion model. By accounting for the buoyancy term, the model accurately predicts the stoichiometric hydrogen flame length within a mere 0.2% deviation from the experimental value. In contrast, excluding the buoyancy term leads to a prediction divergence of around 5%. Deeper analysis of the mixture fraction field indicates that buoyancy enhances mixing in the flame's far -field region, facilitating a more rapid dilution of the fuel stream within the air. This, in turn, results in a shorter flame. The scope of the modelling is expanded to encompass buoyancy effects on hydrogen flames with jet Reynolds numbers (ReJ) up to 15,000. While the buoyancy's influence on flame control weakens as ReJ increases, a noticeable similar to 4% variation in stoichiometric flame length persists between scenarios with and without buoyancy.