Effects of swirl intensity on flame stability and NO emission in swirl-stabilized ammonia/methane combustion

Ammonia is an attractive clean fuel for its potential to reduce CO2 emission and fossil fuel consumption. However, ammonia combustion has been mainly discouraged by the low flammability and the high fuel NOx emissions. This study numerically investigates the effects of swirl intensity on combustion characteristics in swirl-stabilized ammonia/methane combustion. Large eddy simulation was performed by using OpenFOAM, and the accuracy of numerical results was validated by the experiment. The results show that swirl intensity will significantly affects the flow field and flame structure, and flame stability decreases with the swirl number increasing. The high swirl intensity leads to extinguishing at the flame root, while the low swirl intensity cannot generate the central recirculation zone to stabilize the flame. Selective non-catalytic reduction of NO (SNCR) is the key to controlling NO emission, the decrease of temperature will promote the reduction of NO, while the decrease of residence time will inhibit the reduction of NO. Meanwhile, SNCR will weaken the correlation between NO and OH in ammonia/methane combustion. NO emission will decrease with the swirl intensity increasing. In a word, medium swirl number (S & AP;0.76) is proper to control NO emission and ensure flame stability.