Experimental investigation of the characteristics of combustion in the full hydrogen blending range of methane-hydrogen mixtures in a MILD model combustor

Abstract

MILD combustion technology is expected to enable safe and stable low-emission combustion of hydrogen-doped fuels, or pure hydrogen fuels, in gas turbines designed for zero-carbon emissions. To improve combustion stability at high hydrogen content while maintaining low NOx emissions, a MILD model combustor was modified, specifically the upstream fuel/air distribution and mixing method. And the combustion stability of the modified MILD combustor was significantly extended. Here, the combustion characteristics of the modified MILD combustor are experimentally investigated at 0–100% hydrogen contents. The investigation results demonstrate that unlike the combustion stability region at low hydrogen concentrations, a narrow thermoacoustic instability region occurs at 60% hydrogen content. As the hydrogen content increases, the instability region becomes narrower while shifting towards lower equivalence ratios. The change in hydrogen content is accompanied by a significant peak energy migration of the dynamic pressure. The OH* chemiluminescence images showed that the heat release zone became more concentrated with increasing hydrogen content. And the dominance of high-frequency peak energy correlates to lateral motion, whereas the dominance of low-frequency peak energy corresponds to axial motion. This transition in flame dynamics occurs not only for different hydrogen contents but also for different equivalence ratios of pure hydrogen combustion. In contrast, NOx emissions are not sensitive to hydrogen content. At the same time, the MILD model combustor produces low emissions, with NOx emissions of less than 10 ppm@15%O2 at adiabatic flame temperatures ranging from 1200 K to 2100 K. These results show that the MILD model combustor has favorable fuel suitability.