A Numerical Investigation of Reheat Hydrogen Combustion in a Simplified Geometrical Configuration from Atmospheric Pressure to Full Load Conditions

An increasing amount of recent experimental evidence indicates that sequential combustion is particularly well-suited for burning highly-reactive fuels like hydrogen, while maintaining low emissions. A convenient feature of the sequential combustion system, resulting in a fundamental advantage compared to alternative approaches, is the possibility of controlling the second-stage flame position through its combustion characteristics, defined by a complex balance of propagation versus spontaneous ignition, based mainly on the reactants’ inlet temperature. At full-load conditions, requiring high pressure and high flame temperature, fuel mixtures with a hydrogen content approaching 100% still bring significant challenges, it is therefore of key importance for the further development of hydrogen-firing capabilities of the gas turbine to improve our present understanding of the interaction between flame propagation and spontaneous ignition and of its role in controlling flame stability and emissions. A series of DNS and LES calculations, featuring complex chemical kinetics and a fully-compressible representation of the reactive flow, are performed on simplified geometrical configurations, yet representative of a sequential combustion system. The present research effort provides novel insight about the combustion characteristics of hydrogen reheat flames at nominal part- and full-load conditions, defining their structure and stabilization mechanism for a range of reactants temperature, as well as modelling guidelines for a reliable numerical approach to reheat combustion.