On NO and N2O formation and conversion in laminar non-premixed jet flame of NH3

This work reports new observation of N2O emission from the laminar non-premixed jet flame of NH3 at liftoff. Considering the simultaneous NO emission decline, two-dimensional simulation is conducted with a selfsimplified kinetic model to give an insight into the formation and conversion mechanism of NO and N2O in both attached and lifted flames. The experimental observations are successfully reproduced, thereby, detailed analyses are conducted with the reaction-transport interaction considered through a species budget method. Liftoff makes a part of the non-premixed reaction zone in the attached flame replaced by two distinct premixed reaction zones, forming a complicated "triple flame" structure. The inner rich premixed reaction zone and the more compact NO formation region in the outer lean-premixed one result in the significant NO emission decline detected in our previous experimental work. N2O forming inside the attached flame cannot slip and cause emission as the formation zone is wrapped by the consumption zones. However, in the lifted flame, particularly in the rolled-up part of the lean-premixed reaction zone, N2O forming locally or imported from the upstream region through convection can be outwardly transported by radial diffusion into the low-temperature region and be preserved there, causing N2O slip and emission.