The flame structure and combustion dynamics in a steam diluted H₂/Air micromix flame

The OH* chemiluminescence is used to investigate experimentally the effects of nozzle diameter (d), steam dilution ratio (D) and equivalence ratio (φ) on flame structure and combustion dynamics in a steam diluted H₂/air micromix burner. Two flame types, anchored and lifted, are found. The OH* signal for the anchored flame primarily presents in flame shear layer zone (SLZ), while that for the lifted flame mainly appears in the flame central recirculation zone (CRZ) and flame tail zone (FTZ). The increase of the velocity of hydrogen (as the D decreasing or the φ increasing) would change anchored flame to lifted flame. The Power Spectral Density (PSD) analysis shows that changing from anchored to lifted flame would result a high OH* fluctuation frequency, which shows the same trend as the decrease of d. The Dynamic Mode Decomposition (DMD) analysis shows that the distribution of dominant mode is similar to the distribution of OH* signal. The SLZ is the primary oscillation zone for anchored flame and the CRZ for lifted flame. The anchored flame is more stabler comparing to the lifted one, and the lifted flame should be avoided in practical burners. Besides, the high mixing intensity of fuel and oxidizer is beneficial to the stability of micromix flame.