Study on the combustion characteristics and stabilization mechanism of low swirl CH₄/H₂ flame

The numerical simulation on the premixed CH₄/H₂ gas at an equivalence ratio of 0.7 was conducted to investigate the combustion characteristics and stabilization mechanism of low swirl CH₄/H₂ flame in various hydrogen volume proportions. The analyses on the self-similar characteristics, the flow field structure and the flame characteristics of CH₄/H₂ flame were performed, and the effect of swirl number on the flashback of hydrogen-enriched fuel was studied. The results showed that with the increase of H₂ volume proportion, the self-similar characteristics of CH₄/H₂ flame still remain; the intensity of the shear layer increases gradually and the inner shear layer moves gradually to the central low-velocity zone, which compels the flame front towards the nozzle, and the shape of the flame changes from the “bowl” type to “W” type, and then converts to “V” type finally. The mean axial and radial aerodynamic stretch rates and the virtual origin are almost not affected by the hydrogen volume proportion. When the hydrogen volume proportion increases from 80% to 95%, the laminar flame speed of the fuel changes greatly, leading to drastic changes in the flow field structure and the flame front. As for the CH₄/H₂ flame in the central low-velocity zone, when the flame propagation velocity is equal to the local gas velocity, the flame is stable; as for the CH₄/H₂ flame in the shear layer, the vortex produced by the velocity gradient facilitates the local gas flowing downward and moving toward the central low-velocity zone, thus the flame moves upward and reaches a stable state. Decreasing the swirl number properly is beneficial to the reduction of the flashback of hydrogen-enriched fuel.