Analysis of thermoacoustic instability and emission behaviors of lean premixed biogas/ammonia flame

Abstract

Ammonia and biogas are promising renewable fuels that can reduce carbon emissions. This paper studies thermoacoustic instability and emission behaviors of biogas/ammonia co-firing swirl flame. The effects of CO₂ proportion in biogas (${{\chi }_{\text{CO}}}_2$), ammonia proportion (${{\chi }_{\text{NH}}}_3$) and equivalence ratio (Φ) on combustion characteristics were considered. A chemical reactor network (CRN) was established to advance comprehension regarding NO emission. The results show that high Φ and ${{\chi }_{\text{CO}}}_2$ are more conducive to simultaneously suppressing thermoacoustic instability and NO emissions. Lower ${{\chi }_{\text{CO}}}_2$ flame appears to have intense thermoacoustic instability when Φ near 0.90, and the instability intensity is significantly weakened when ${{\chi }_{\text{CO}}}_2$ exceeds 20%. The CO₂ in the mixture inhibits NO formation but promotes CO formation. The CRN results show that CO₂ in biogas reduces NO emissions by inhibiting the HNO pathway and promoting the NHi pathway. This study furnishes a foundation for advancing clean and efficient low-carbon combustion systems.