Mixing Performance of Adjustable High Flame Speed Injector Configurations and NOx Emissions From a Recuperated Gas Turbine Operated on 100% Hydrogen

Abstract This work extends previous work on an high flame speed (HFS) injector design that allowed successful operation of a Capstone 65 kW MTG on 100% hydrogen without flashback from cold start to full power to shut down. Two new versions of the HFS injector are investigated in this work. An adjustable fuel distributor allows control of the axial location within the injector where the fuel and air begin to mix. Additionally, the new designs allow different amounts of air to be admitted into the mixing section where mixing with hydrogen takes place. This provides adjustment of mixing time and fuel/air ratio within the injector which, in principle, can reduce NOx emissions by reducing fuel rich areas at the injector outlet. Fuel concentration maps are measured at the exit plane for 3 injector configurations which set the fuel distributor at different axial locations and different amounts of open area for air inlet. The experimental work is complemented by high fidelity simulations which provide additional details about the injector flow field and dynamic mixing behavior. Notably, the injector open area did not dramatically change the velocity of the air at the exit plane which is a result of an air guide that is the limiting area for the air flow. Further, the configurations studied did not result in significantly improved fuel/air mixing as expected. One injector configuration was tested in the engine and the measured NOx emissions exhibited an increase compared to the baseline design which is consistent with the observed mixing performance. The results show that, despite adjusting the mixing strategy within the injector, reduction in air momentum associated with the increase in open area degrades the fuel/air mixing performance. Thus, while additional successful operation of a premixed approach on 100% hydrogen is demonstrated, further effort is required to attain the desired low NOx emission levels. Consistent results between the CFD and experimental injector results indicates utility of the CFD for guiding future designs.