Influences of different diluents on NO emission characteristics of syngas opposed-flow flame

This paper used the opposed-flow flame model and GRI 3.0 mechanism to investigate NO emission characteristics of H₂-rich and H₂-lean syngas under diffusion and premixed conditions, respectively, and analyzed influences of adding H₂O, CO₂ and N₂ on NO formation from the standpoint of thermodynamics and reaction kinetics. For diffusion flames, thermal route is the dominant pathway to produce NO, and adding N₂, H₂O and CO₂ shows a decreasing manner in lowering NO emission. The phenomenon above is more obvious for H₂-rich syngas because it has higher flame temperature. For premixed flames, adding CO₂ causes higher NO concentration than adding H₂O, because adding CO₂ produces more O radical, which promotes formation of NO through NNH + O = NH + NO, NH + O = NO + H and reversed N + NO = N₂ + O. And in burnout gas, thermal route is the dominant way for NO formation. Under this paper's conditions, adding N₂ increases the formation source of NO as well as decreases the flame temperature, and it reduces the NO formation as a whole. In addition, for H₂-lean syngas and H₂-rich syngas with CO₂ as the diluent, N + CO₂ = NO + CO plays as an important role in thermal route of NO formation.