SUMMARYA numerical study with momentum-balanced boundary conditions has been conducted to grasp the chemical effects of added CO 2 to fuel-and oxidizer-sides on flame structure and NO emission behaviour in H 2 -O 2 diffusion flames with varying flame location. A reaction mechanism is proposed to show better agreements with experimental results in CO 2 -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 CO 2 . The present work also displays separately thermal contribution and prompt NO emission due to the chemical effects caused by thermal dissociation of added CO 2 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.

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