Environment-dependent dual role of ammonia on the radiative characteristics of single-pellet biomass co-firing

Abstract

Co-firing ammonia (NH₃) with biomass is a promising decarbonization strategy, yet its influence on crucial radiative heat transfer characteristics remains poorly understood. To address this, the dynamic effects of NH₃ addition on the flame characteristics of single rice husk pellets were investigated using an in-situ coupled spectroscopy-imaging diagnostic technique under various temperatures and oxygen concentrations. Results showed that NH₃ addition shortened the ignition delay time but significantly suppressed the flame temperature, size, and radiation intensity during the main combustion stage. A novel, environment-dependent “dual role” of NH₃ on radiative properties was discovered: at a lower temperature (700 ℃), NH₃ enhanced both spectral radiation intensity and exergy, whereas at higher temperatures (800 − 900 ℃), it exerted a significant inhibitory effect. Furthermore, increasing NH₃ concentration monotonically suppressed the characteristic atomic emission of alkali metals (K*, Na*), while the chemiluminescence of NH₂* radicals was selectively observed only under high-temperature, oxygen-lean conditions (900 ℃, 10 vol-% O₂). These findings reveal the complex, coupled influence of NH₃ on biomass combustion and provide a critical theoretical basis for the optimization of NH₃/biomass co-firing technology.