Novel Fuel Injector Geometry for Enhancing the Fuel Flexibility of a Dry Low NOx MicroMix Flame

A novel fuel injector is presented for enhancing the fuel flexibility of the dry micromix (MMX) combustion principle. Originally having been developed for pure hydrogen fueling, the micromix combustion is based on a non-premixed type jet-in-crossflow mixing for inherent safety against flashback, as well as flame miniaturization and multiplication for suppressing NOx emissions. This study investigates the potential of the novel geometry regarding the operation with higher natural gas content fuels. In experiments at atmospheric pressure conditions it could be shown that the new injector extends the fuel flexibility down to between 60 and 80 vol.% H2. The responsible flow phenomena are verified with numerical RANS simulations at engine pressure conditions using a detailed chemistry model. An experimental validation of numerical methods at atmospheric conditions based on OH chemiluminescence distributions showed that the unsteady LES model can predict the micromix flame more accurately regarding to its ignition point than the steady RANS model, although the reaction progress is underestimated by both models, which in comparison to the experiment results in a more stretched flame.