Numerical investigation of the mixing and combustion in a partially premixed swirl-stabilized hydrogen flame

Abstract

In this thesis the results of mixing and combustion simulations with the premixed famelet method are presented and discussed. They were obtained by large-eddy simulations of a technically premixed swirl-stabilized hydrogen burner with axial air injection. The burner was developed by Reichel et al. [32, 33, 30, 31] to operate under lean conditions on highly reactive fuels such as hydrogen or syngas. The aim of the simulations was to improve the understanding of the flame stabilization mechanisms, while simulating the entire technical premixing process,which has not been done before. The investigation was therefore separated into a non-reacting and a reacting analysis. From the non-reacting analysis it became clear that the central axial velocity deficit could not be overcome over the entire length of the mixing tube. This led to vortex breakdown partially in the mixing tube, probably favoured by a fuel-rich central zone. The analysis on the influence of transport properties showed that different Lewis numbers do not have an influence on the isothermal flow. The simulation of the reactive flow was done using premixed flamelets and clearly showed that the flame tip stabilizes inside the mixing tube. An increase in axial velocity at the centerline, caused by the heat release over the flame front, was identified as mechanism which resisted against flashback in the simulation.