Experimental Investigation on the Effect of Nozzle Bluntness Thickness on the Combustion Characteristics of a High-Speed Parallel Jet Mild Combustor

Abstract The safe, stable, and low-emission combustion of high-content hydrogen and pure hydrogen fuels is a crucial aspect of the gas turbine combustion system for achieving carbon-neutral and ultimately carbon-free combustion. However, employing high hydrogen content and even hydrogen as a fuel in combustors presents unique challenges due to distinct fuel characteristics compared to natural gas. This study parametrically investigates the impact of three different nozzle bluntness thicknesses on the reaction zone morphology, combustion stability, and NOx emission characteristics of the high-speed parallel jet MILD combustor. The findings demonstrate that the effect of bluntness thickness variation on the reaction zone morphology can be classified into two distinctive stages: the reaction zone morphology is dominated by the flow field at relatively low hydrogen content and equivalence ratios and by the chemical reactivity of the reactants at higher hydrogen content and equivalence ratios. Meanwhile, the change in lip thickness affects combustion stabilization. The trend of the dynamic pressure main frequency with hydrogen contents and equivalence ratios for the combustor with different lip thicknesses varies in the same way that the trend of the liftoff height of the reaction zone does. Despite significant differences in thermoacoustic characteristics among different bluntness thicknesses, total nitrogen oxide emissions remain relatively unchanged. Total NOx emissions were all less than 10 ppm@15%O2 when the combustion chamber adiabatic flame temperature was less than 2000 K.