Flame stabilization and pollutant reduction of NH₃/Air premixed flame with ethanol spray in a tangential swirl combustor

This work aims to establish a stable premixed ammonia/air flame in a tangential swirl combustor by employing an ethanol spray to extend the fuel-lean extinction limit of the ammonia flame and reduce pollutant emissions. A Planar Laser Induced Fluorescence (PLIF) system is introduced to acquire the flame structure of this blending system. The results demonstrate that OH radicals originating from the ethanol flame support the ammonia flame, in which fluorescence images are indicated by the NH₂ radicals. Moreover, the lean extinction limit is significantly extended from an equivalence ratio of 0.6 to 0.1. In particular, the addition of a minor quantity of ethanol (3 mL/min) to ammonia flame sustains the blending flame due to the ultralow extinction limit of the ethanol swirl spray flame. However, both experimental data and chemical reaction analysis reveal that an increase in OH radical concentration leads to an elevation in NO_x (nitrogen oxides) concentration. This poses a challenge in balancing the effects of ammonia consumption and NO_x generation in the blending combustion system. Ethanol flames indeed generate active radicals (O, OH, HO₂, etc.) to accelerate ammonia oxidation. However, these active radicals also exacerbate the reaction between NO and NO₂, inhibiting their conversion to N₂. Even so, the objective of achieving clean combustion with low concentrations of both NO_x and unburned NH₃ can still be met under the condition of the total air flow rate 90 L/min and the global equivalence ratio 0.7.