EINOx scaling in a non-premixed turbulent hydrogen jet with swirled coaxial air

The effect of swirl flow on pollutant emission (nitrous oxide) was studied in a non-premixed turbulent hydrogen jet with coaxial air. A swirl vane was equipped in a coaxial air feeding line and the angle of the swirl vane was varied from 30 to 90 degrees. Under a fixed global equivalence ratio of φ G = 0.5, fuel jet air velocity and coaxial air velocity were varied in an attached flame region as u F = 85.7–160.2 m/s and u A = 7.4–14.4 m/s. In the present study, two mixing variables of coaxial air and swirl flow were considered: the flame residence time and global strain rate. The objective of the current study was to analyze the flame length behavior, and the characteristics of nitrous oxide emissions under a swirl flow conditions, and to suggest a new parameter for EINOx (the emission index of nitrous oxide) scaling. From the experimental results, EINOx decreased with the swirl vane angle and increased with the flame length ( L). We found the scaling variables for the flame length and EINOx using the effective diameter ( d F ,eff) in a far-field concept. Normalized flame length ( L divided by d F ,eff) fitted well with the theoretical expectations. EINOx increased in proportion to the flame residence time (∼ τ R 1/2.8) and the global strain rate (∼ S G 1/2.8).