Kinetic Analysis of NO Formation in Axial Air-staged NH3/CH4 Combustion
One of the foremost challenges faced by NH3/CH4 mixed fuel is the substantial formation of fuel-NOx during combustion.Axial air-staged combustion has been experimentally proved effective in mitigating NOx in ammonia-blended fuel.However,there is a lack of understanding of the intrinsic correlations between the optimal equivalence ratio of primary combustion chamber and final NOx formation.This study focused on a 50 kW micro gas turbine combustion chamber and employed the Chemkin-Pro code to investigate the impacts of primary equivalence ratio on NOx emissions in NH3/CH4 axial air-staged combustion,as well as the underlying kinetic mechanism behind the optimal equivalence ratio.The results indicate that the optimal equivalence ratio represents a tradeoff between NO production and fuel consumption in the primary zone.HNO emerges as the major precursor of NO during combustion of ammonia-blended fuels across the studied range of equivalence ratios,but a decrease in which significantly exacerbates the HNO reaction rate.Moreover,when the primary equivalence ratio exceeds 1.21,the consumption of combustible products such as HCN,H2,and CO from the primary zone produces O and OH free radicals in the secondary zone,causing rapid formation of NO.
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