The Design and Optimisation of a 100% Hydrogen Micro Gas Turbine Micromix Combustor: Preliminary Hydrogen Injection Depth Characterisation Using Cold Flow Steady RANS

Abstract

In a modern electricity grid, with fluctuating renewable energy input and problems linked to construction of large power plants in densely populated areas, local, flexible, and zero-emission electricity and heat production becomes evermore important. Consequently, we research the design and optimisation of a hydrogen fuelled micro Gas Turbine (mGT). This paper focusses on our continued development and optimisation of the low-NOx hydrogen combustion chamber, based on the Micromix principle. Based on previous work, we observed that the hydrogen injection depth was critical in minimising thermal NOx formation. To characterise the hydrogen Jet in Cross Flow (JICF) mechanism more deeply, we first designed a simplified single nozzle variant of the micromix geometry. Using this test geometry, we analysed the relation between the hydrogen injection pressure and the hydrogen injection depth, perpendicularly into the air flow, using both an analytical model and cold flow steady RANS simulations. From these simulation results we obtained a preliminary optimal range for the injection pressure, so that the hydrogen does not protrude too far into the air stream (thereby increasing the residence time and increasing the possibility of higher thermal NOx formation), nor too little (thereby reducing the mixing of both fuel and air and increasing the chance of combustion too near to the wall). Based on these results, we can, using hot flow steady RANS simulations, validate the optimal hydrogen injection pressure range from the single-nozzle, cold flow results, for minimal thermal NOx formation, in a follow-up research.