The effect of turbulence intensity of ambient air flow on NO_x emissions in H₂/air nonpremixed jet flames

The effects of turbulence intensity of an ambient air flow on flame structure and NO_x formation were investigated experimentally in hydrogen/air nonpremixed flames. To identify the effect of sole turbulence intensity, a new combustor with a turbulence generator, which can increase the turbulence intensity of air stream under the condition of an identical mean velocity, was adopted. The experiment was conducted with and without the turbulence generator for the two fuel cases of H₂ : N₂ = 1 : 1 and H₂ : N₂ = 1 : 2, by volume. As a result, as the turbulence intensity increased, the reducing effect of NO_x was more significant in the condition of a higher flame temperature. In addition, the conversion ratio from NO to NO₂ increased. Two major factors can reduce the production of NO_x as the turbulence intensity increases: significant NO_x reduction corresponding to about 70% was found in the upstream region due to the increase in the strain rate effect and in the downstream region due to the rapid mixing effect. From these results, it is possible to conclude that adjustment of turbulence intensity is a very useful method to reduce NO_x emission in hydrogen nonpremixed jet flames.