Comparison of combustion characteristics of MILD model combustor and multi-nozzle array model combustor fueled hydrogen-methane mixtures

Abstract

Key issues facing the development of hydrogen gas turbines include achieving low NOx emissions on hydrogen-enriched fuels, prevention of flashback and thermoacoustic instability. The present experimental investigation shows the fuel feasibility of MILD combustion and multi-nozzle array combustion with hydrogen-enriched fuels. The combustion characteristics, such as the range of combustion stability, NOx/CO emissions, and reaction zone distribution, have been determined for hydrogen contents ranging from 0% to 50% by volume. Compared to the MILD model combustor, the multi-nozzle array model combustor can achieve a broader range of stable combustion up to 40% by volume. As the hydrogen content increases from 0% to 40% by volume, the lean blowout (LBO) temperature of the multi-nozzle array model combustor decreases from 1600 K to 1400 K. When the hydrogen content reaches 50% of the volume, both the MILD model combustor and the multi-nozzle array model combustor exhibit thermoacoustic instability at high equivalence ratios. For the multi-nozzle array model combustor, NOx emissions are less than 20 ppm@15% O2 and CO emissions are less than 30 ppm@15% O2 in the adiabatic temperature range of 1400 K–2100 K. NOx emissions of the multi-nozzle array combustor are higher than that of the MILD combustor, but remain ultra-low due to the flue gas recirculation ratio. With increasing hydrogen content, the reaction zone becomes more concentrated along the axial and radial directions. The lift-off height of the reaction zone is 1.6 nozzle diameters at 40% by volume hydrogen content, which ensures the safety of the nozzles and prevent flashback.