A numerical study on NO emission in bluff-body stabilized swirl diffusion flames

The combustion characteristics of the methane blended bluff-body stabilized swirl diffusion flames within the turbulent regime are studied numerically with a coupled flamelet/radiation approach along with a modified k-ε turbulence model to determine the effect of swirl number on the flame dynamics and NO emission. The selected flames are controlled by changing the bulk tangential velocity of the swirl annulus whilst they possess the same operating conditions.

Two different structures are observed by changing the swirl intensity. Flames with low swirl number (Sg=0.3) showed a radially converged shape in downstream. With increasing the swirl number a downstream recirculation zone is appeared due to vortex breakdown formation which provides an hourglass shape with open tails. However, the flame length is inversely related to the swirl number. Furthermore, results show that NO emission profiles are strongly analogous to the temperature distribution which demonstrates the thermal NO formation. The NO mass fraction values in the near-field and far-field regions are investigated with fuel enrichment. It is found that increasing the H/C atoms at the inflow diminishes the NO level.