Influence of Air/Hydrogen Momentum Ratio, Equivalence Ratio and Dilution Hole Geometry on the Performance of a Micromix Combustor for a 100 kWe mGT

Against the background of a growing deployment of renewable electricity production, like wind and solar, the demand for energy storage will only increase. One of the most promising ways to cover the medium to long-term storage is to use the excess electricity to produce hydrogen via electrolysis. In a modern energy grid, filled with intermittent power sources and ever-increasing problems to construct large power plants in densely populated areas, a network of Decentralised Energy Systems (DES) seems more logical. Consequently, building a previous work, there is a need for 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, using steady-state RANS CFD simulations. To further optimise the primary zone of the combustor, this work concentrates on the specific impact of the air/fuel momentum ratio, the primary zone equivalence ratio and dilution zone geometry on the combustor performance. First, the air mass flow rate and the hydrogen inlet pressure are varied within a specified control range. This results in a range for the momentum ratio and the equivalence ratio for which we can analyse the resultant NOx concentration at the combustor outlet. This allows the momentum ratio and the equivalence ratio to be optimally chosen for a new primary zone combustor geometry with lower NOx formation. In a second step, this primary zone design is completed with an initial and separately optimised design of the secondary air zone or dilution zone. An analysis was made on the variation of several key dilution zone design parameters such as; the diameter of a dilution hole, the number of dilution holes in a single row, the variation in size between the holes in the same row and the distance from the centre of the single row of dilution holes to the combustor head. This parameter variation study affected the secondary air mass flow rate, the average outlet temperature, the outlet temperature homogeneity and the NOx emissions at the combustor outlet, on the basis of which a first simple, single dilution hole row is proposed and optimised. Both the final optimisation of the primary zone and the optimisation of the secondary zone will come together a new micromix combustor geometry that will be part of the future work and will be included in the presentation at GT2023.