Comparative study of flame structures and NO_x emission characteristics in fuel injection recirculation and fuel gas recirculation combustion system

A numerical study with momentum-balanced boundary conditions has been conducted to grasp the chemical effects of added CO₂ to fuel- and oxidizer-sides on flame structure and NO emission behaviour in H₂–O₂ diffusion flames with varying flame location. A reaction mechanism is proposed to show better agreements with experimental results in CO₂-added hydrogen flames.

Oxidizer-side dilution results in significantly higher flame temperatures and NO emission. Flame location is dramatically changed due to high diffusivity of hydrogen according to variation of the composition of fuel- and oxidizer-sides. This affects flame structure and NO emission considerably especially the chemical effects of added CO₂. The present work also displays separately thermal contribution and prompt NO emission due to the chemical effects caused by thermal dissociation of added CO₂ in NO emission behaviour. It is found that flame temperature and the flame location affect the contribution of thermal and prompt NO due to chemical effects considerably in NO emission behaviour. Copyright © 2004 John Wiley & Sons, Ltd.