Micro Mixing Fuel Injectors for Low Emissions Hydrogen Combustion

The consideration of hydrogen as a fuel for next generation low emissions gas turbines raises a number of challenges and potential benefits relative to the combustion system. The present work examines the use of a micro-mixing injection strategy for hydrogen as a means to achieve rapid mixing and inherent flexibility for accommodating various staging, dilution, and dual fuel requirements for future gas turbine engines. The work presented includes numerical and experimental results associated with the fuel-air mixing process in a representative injector configuration. Measured NOx emissions and fuel/air ratios at the exit of the mixer are shown along with visualization of the reactions generated. Detailed computational fluid dynamics (CFD) is used in parallel to elucidate the behavior of the flow inside and downstream of the injectors. Results are also presented for natural gas to provide a point of reference. The results illustrate a number of interesting features and characteristics of the hydrogen/air mixtures which are in dramatic contrast to the behavior of natural gas/air mixtures. Comparison of the measured and modeled mixing behavior illustrates a number of challenges associated with the selection of a robust modeling approach for hydrogen/air combustion. The results demonstrate that the use of micro-mixing fuel injection to achieve ultra low NOx emissions is very promising.