Three-dimensional analysis of hydrogen fuel effects in multi-tube combustor

Flame characteristics, including mixing and stabilization in a multi-tube micromixer (MTM) combustor operating with hydrogen fuel are analyzed using high-fidelity simulations. In this flow configuration, a bundle of tubes issue fuel-air mixture into a combustion chamber, leading to multiple flame fronts, which may interact in an unsteady manner. Highly-resolved simulations enabled by adaptive mesh refinement with detailed kinetics are used. The results are first validated against experimental data for both a methane–hydrogen blend and pure hydrogen fuel, showing very good agreement with experimental image data. A detailed analysis of the hydrogen case reveals that global flame structures display distinct shapes across various flow streams. Upstream jet interactions induce mixture stratification along the tubes that is amplified with geometry-induced flow strain in the main chamber. These composition and fluid transients result in unsteady shear layer reactions of varying intensities that promote the recurrent formation of flame pockets and fuel filaments. Although transient flow effects are pronounced near the tube exit, an elongated primary reaction zone is observed for the central tube, the reaction zone being approximately 30% wider in the transverse direction where neighboring tubes are further apart. In addition, streamlines and velocity quiver plots highlight flow asymmetries that interact with heat release in primary flame reaction zones for near-wall tubes, while the central region maintains a predominantly uniform flow, resulting in securely anchored flames during adjacent flame oscillations. The study emphasizes that collective flame dynamics, rather than isolated local behavior, is key to achieving stable operation in such tubular bundled burners.