Elucidating ammonia's impact on non-gray radiation and thermometry during biomass co-firing via spectral guidance

Ammonia co-firing with biomass is a vital strategy for decarbonizing power generation, yet optimizing its efficiency and emissions necessitates accurate flame temperature monitoring. Reliable diagnosis, however, is impeded by strong, phase-dependent non-gray radiation from biomass (volatile vs. char) and the critically unquantified impact of NH₃ on essential spectral radiative properties. This work systematically investigates the influence of NH₃ concentration on the spectral emissivity ε(λ) of burning rice husk particles within the visible spectrum (400–700 nm) during distinct volatile and char combustion phases, utilizing simultaneous spectroscopy and RGB pyrometry. The investigation revealed that NH₃ significantly lowers ε(λ) for both volatile combustion, where ε_λ decreases with wavelength (ε(λ) < 0.16), and char combustion, where ε_λ increases with wavelength (ε(λ) ≈ 0.35–0.75). Consequently, the key emissivity ratio ε_g/ε_r (at 530/600 nm) required for RGB pyrometry exhibited opposite behaviors: for volatile combustion, ε_g/ε_r > 1 and increased with NH₃ concentration, whereas for char combustion, ε_g/ε_r < 1 and decreased with NH₃ concentration. Building upon these quantitative findings, the developed and validated spectrally-guided RGB pyrometry methodology successfully corrects the substantial temperature overestimation inherent in the gray-body assumption, an error particularly pronounced at higher NH₃ concentrations. This work yields both fundamental quantitative data on ammonia's impact on biomass non-gray radiation and a robust spectrally-guided diagnostic method, providing essential data and techniques for enabling accurate modeling, optimization, and control of biomass-ammonia co-firing processes.