Optical investigations on hydrogen/methane‑oxygen flame diluted by steam in micro-mixing burners

Motivated by the goal of zero-emission power generation, the current paper investigates the micro-mixing combustion of hydrogen/methane and oxygen under steam diluted conditions, over a range of oxygen mole fraction (0.05–0.5) and hydrogen blending power ratios (0–100%). The intensified OH* chemiluminescence technique, coupled with planar laser-induced fluorescence (PLIF) of the OH radical and acetone, as well as water vapor emission spectrum measurement, were employed to capture the flame structure, fuel concentration fields and temperature. Analysis of the inlet parameters reveals that oxygen mole fraction predominantly influences the momentum ratio (by nearly two orders of magnitude) and burning velocity (a reduction of 98%), whereas the hydrogen blending power ratio primarily affects the effective Lewis number (a reduction of 55%) and burning velocity (an increase of 300%). The combustion stability map further demonstrates that increasing the hydrogen blending power ratio substantially widens the flame stability limits. Steam dilution within the combustion chamber yields a uniform temperature field, with peak temperatures remaining compliant with gas turbine material limits. Furthermore, investigation of the cold-flow mixing and flame dynamics indicates that a larger mixing distance leads to more uniform fuel distribution at the exit, thereby enhancing flame stability. The introduction of swirl enhances circumferential spreading of fuel acetone and flame OH at the nozzle exit, which leads to a weakening of the flame root. The seven-nozzle array achieved stable combustion at a thermal power of ∼3.6 kW across a hydrogen-blending ratio range of 40%–100% and it was observed that higher ratios weaken adjacent-flame interactions.