Characterization of a 5-nozzle array using premix/micromix injection for hydrogen

Hydrogen is one of the most promising fuels to decarbonize energy systems since it has a high specific energy, a carbon-free combustion process, and may be produced sustainably through electrolysis. Direct fuel drop-in replacement cannot be done in traditional lean, premixed combustion burners because of the high reactivity of the hydrogen-air mixture and its inherently unstable nature that might lead to flashbacks and hardware failure. Consequently, new injection strategies, and burner geometries, are investigated to mitigate these risks. Here we present the hydrogen capabilities of the premix/micromix injector that relies on a two-staged fuel injection strategy to offer wide fuel flexible capability (methane to hydrogen) within a single design. Five injectors are placed in a cross-shaped array to simulate a sector found in multi-element combustion systems. Stability and combustion dynamics maps are obtained for the array and OH planar laser-induced fluorescence (PLIF) provides additional insights into the combustion process of these novel burners when placed in an array. The use of micromixing is shown to drastically improve the acoustics of this geometry and expand the flashback limits compared to a fully premixed configuration. Significant variability in flashback limits are observed for different additively-manufactured injector configurations. Phase-averaged OH-PLIF measurements, obtained by registering the acquisition with the acoustics module, and the 3D reconstruction of a partially-premixed flame highlight the complexity of the stabilization mechanisms for these highly three-dimensional, non-axisymmetric flames that may be subjected to large thermoacoustics. This first investigation into premix/micromix clustered injectors demonstrates the importance of better understanding the impact of flame-flame interactions in multi-element combustion systems with micromixed, or partially-premixed, combustion.