An Investigation of a Multi-Injector, Premix/Micromix Burner Burning Pure Methane to Pure Hydrogen

Micromix combustion technology has been identified as a promising strategy to mitigate the risks associated with burning high-hydrogen-content fuels. This technology has recently been introduced in premixed injector designs to develop burners with broader fuel flexibility, allowing the combustion of fuels ranging from natural gas, or currently available hydrocarbons, to pure hydrogen by controlling the micromix fuel ratio (MFR). Modifying this additional operating parameter can lead to premixed, partially premixed, and micromixed combustion, each having different stability mechanisms. The combustion characteristics of such flames in an industrial combustion environment with hundreds of injectors are unknown. A multi-injector configuration, consisting of five (5) injectors placed in a cross pattern, is used to investigate the combustion of pure methane to pure hydrogen, and different blends. Stability and combustion dynamic maps are first obtained at atmospheric temperature and pressure for fuel-lean mixtures of H₂/CH₄ ranging from 0/100%, 70/30%, 90/10%, to 100/0%, by volume. For each fuel mixture, the equivalence ratio is adjusted to maintain the same adiabatic flame temperature throughout the experiments. An increase in blowoff (BO) limit is observed for the multi-injector array compared to a single nozzle, while flashback occurs more rapidly for dominantly premixed conditions with high-hydrogen-content fuel. In addition to extending the flashback limit, micromixed flames are generally quieter for high-hydrogen-content fuels. Laser diagnostics are performed on selected operating conditions with hydrogen content of 0%, 30%, 50%, 70%, 90%, and 100%. Eight cases are investigated in this work at a constant bulk inlet velocity to highlight the impact of hydrogen content and MFR on the flame shape. Two-dimensional (2D) particle image velocimetry (PIV), OH and acetone planar laser-induced fluorescence (PLIF), as well as acoustic measurements are performed simultaneously. The planar measurements show that the OH-PLIF signal becomes thinner and nonaxisymmetric as MFR is increased from 0% to 100%, with the flames gradually transitioning from V-shaped to M-shaped, before stabilizing as jet flames in crossflow.