Experimental study of coupling characteristics between flame dynamics and CO emissions using wavelength modulation spectroscopy

The coupled characteristics of flame dynamics and emissions in energy systems are critical for understanding combustion instability mechanisms and implementing effective emission control, necessitating high temporal-resolution optical diagnostic methods for dynamic, in-situ measurement of combustion products. This study experimentally investigates the coupling characteristics between flame dynamics and CO emissions in a centrally staged combustor using wavelength modulation spectroscopy (WMS). The developed WMS measurement strategy provides millisecond-resolution insights into the fluctuations of CO emissions, while simultaneous flame imaging was performed using high-speed OH* chemiluminescence. As the staging ratio increases, the flame in the central recirculation zone intensifies and interacts with the shear-layer flame, resulting in combustion instabilities. The dominant frequency of CO fluctuations at 267 Hz is coupled with both the acoustic pressure and flame intensity. The dynamic CO emissions are correlated to the overall flame intensity and axial convective motion by coherent flame modes analysis. Periodic heat release and localized flame quenching are identified as the primary sources of CO fluctuations. This work contributes to a deeper understanding of the coupling mechanisms between flame dynamics and emissions in centrally staged combustion systems, offering valuable guidance for the synergistic control of combustion instability and pollutant formation.