DEVELOPMENT OF FLASHBACK RESISTANT LOW-EMISSION MICRO-MIXING FUEL INJECTOR FOR 100% HYDROGEN AND SYNGAS FUELS

The present work extends previous efforts using "micro-mixing" fuel injectors operating on hydrogen fuel to elevated pressure and temperature and includes initial evaluation of a second injector concept. A micro-mixing fuel injector consists of multiple, small and closely spaced mixing cups, within which fuel and air mix rapidly at a small scale. The micro-mixing injection strategy offers inherent flexibility for the accommodation of staging, dilution, and fuel flexibility, and the manufacturing technology employed for building the cups affords great flexibility to address the conflicting demands of superior fuel-air mixing and flash-back avoidance. In the present work, both radial and axial flow micromixing concepts are investigated using experiments and computational fluid dynamics. The hydrogen/air reaction structure is captured using OH* chemiluminescence at 308 nm, recorded using a 16-bit thermoelectrically cooled ICCD with a UV sensitive phosphor. Instantaneous images are used to assess flashback tendencies at pressures up to 8 atm for reaction temperatures approaching 2000 K. Emissions are measured at the exit of the combustor liner using EPA certified methodologies. The results demonstrate that both concepts can produce low NOx emissions while remaining robust relative to flashback and lean blowout. The radial concepts offer superior emissions performance, while the axial concepts offer superior flashback tendencies. Based on the results obtained to date, the micromixing approach appears promising relative to achieving flashback free operation with low emissions at pressures up to 8 atm while maximizing scalability and fuel flexibility.