The Structure And Stability of Premixed CH4, H2, and NH3/H2 Flames in an Axially Staged Can Combustor

Abstract An experimental investigation of flame structure, stability, and emissions performance was conducted in a two-stage combustor design operated with CH4, H2, and NH3/H2 fuel blends. The main flame zone features a premixed bluff body stabilized flame, with a secondary premixed opposing jet flame. The total power and air flow rate are kept constant between the different fuelling cases, while the air split between stages and equivalence ratios are varied to explore conditions relevant to gas turbine operation. Special emphasis is given to analysing the structure of the opposing jet flames in the secondary stage. In contrast to previous literature on reacting jets in cross flow, these interact significantly due to their proximity, leading to a merged flame zone(MFZ) at the impingement layer in the centre of the combustion chamber. As the jet-to-crossflow momentum ratio increases, the MFZ changes shape, reaching close to the walls for the methane cases, but remaining very compact when operating with almost pure hydrogen. For the hydrogen flames, diverting more air to the second stage allows higher total thermal power conditions to be reached, while avoiding flashback and instability. For ammonia-hydrogen flames, the fuel is kept in the primary zone, resulting in some locally rich conditions when air is diverted to the secondary. A local NOx minima occurs when the primary flame is operated at an equivalence ratio of 1.15. Analysis of the flame structure links decreasing NOx to NH3 pyrolysis, followed by a secondary H2 inverse diffusion flame.