Analysis of the NOx Emissions Deriving From Hydrogen/Air Combustion in a Swirling Non-Premixed Annular Micro-Combustor

The objective of this paper is to analyse the thermal performances and emission levels of a swirling non-premixed annular micro-combustor. A three-dimensional simulation of the internal flow in an annular combustion chamber fuelled by hydrogen/air in non-premixed conditions was carried out through Ansys Fluent 2020 R2. A detailed mechanism involving many species and reactions was required to represent the complexity of the combustion process. A 19-reactions and 9 species mechanism was deemed to be appropriate to predict the combustion characteristics with great accuracy and limited processing resources. The reaction mechanism was implemented in Fluent through Chemkin. This model was then compared with the built-in model of the chemical kinetics, which involves just one reaction. The results showed that the 19-reactions model is more accurate to reproduce the centerline temperature distribution than the default simpler model: the 1-reaction model differs by 230 K compared to the experimental data, while the 19-reactions one only by 80 K. The comparison between the velocity of the mixture inside the combustor with and without combustion was also carried out, providing an estimate of the influence of temperature on the flow field. Finally, to meet the emission limits established by the European Commission in 2015, the thermal NOx and NOx derived by NNH were examined on both the outlet and the centerline of the combustor. The study reveals great potential of hydrogen mixtures in reducing emissions and provides insights on the cooling requirements to guarantee wall materials reliability.