Investigation on the coupling mechanism of streamwise and jet vortices of hydrogen micromix combustion

Hydrogen is one of the most promising fuels for achieving zero carbon emissions in civil aviation. However, the rapid flame speed would easily lead to flashback issues, and its ultra-low density would weaken the jet penetration capabilities. Additionally, the high flame temperature during hydrogen combustion tends to produce significant amounts of NOx. To address these challenges, this paper proposes a honeycomb micromix diffusion combustion scheme that enhances mixing through the coupling of air streamwise vortex (ASV) and hydrogen jet vortex (HJV). The micromix element incorporates a disturbance vortex generator (DVG) embedded within a hexagonal microchannel to promote mixing uniformity. Numerical simulations were conducted to analyze the flow characteristics and combustion mechanisms of the DVG perturbation scheme, elucidating the low-emission principles of the micromix diffusion combustion design. The vortex-vortex coupling and vortex-flame coupling effects on the mixing quality were thoroughly analyzed. The DVG creates ASVs within the main airflow, forming an intensely turbulent stirring zone and accelerating the axial velocity decay. The HJV entrains mainstream air, forming a coupled vortex between the HJV and the ASV, which further enhances mainstream disturbance. Uniform mixing within a 30 mm axial length could be achieved and the HJV tube surface approaches an approximate premixed state and results in low NOx emissions.