The Effects of Fuel and Air Mixtures in Non-Premixed Combustion for a Bluff-Body Flame

The bluff-body stabilized flame is used in a numerical study of the non-premixed flames. This paper shows numerical investigations on the effects of hydrogen compositions and nonflammable diluent mixtures on the combustion and NO emission characteristics of syngas non-premixed flames for a bluff-body burner. The assessment of turbulent non-premixed combustion modeling techniques is presented and discussed. The simulations study the predictive capabilities of five turbulence models and are compared with the experiments of Correa and Gulati [1] for a non-premixed flame of 27.5%CO/32.3%H₂/40.2%N₂ and air. The Realizable k-ε and the Reynolds Stress (RSM) models were found to perform the best. Based on this, a numerical study to assess the effects of hydrogen component on syngas non-premixed combustion was performed. As a result, hydrogen addition caused the radial velocity and strain rate to decrease, which was important for mixing to decrease NO. Also, the effectiveness of nonflammable diluent mixtures, including N₂, CO₂ and H₂O, were characterized in terms of the ability to reduce NO emission in syngas non-premixed flames. Results indicated that CO₂ was the most effective diluent to reduce NO emission and H₂O was more effective than N₂. CO₂ diluent produced low levels of OH radical, which makes CO₂ the most effective diluent. Although H₂O increased OH radicals, it was still effective to decrease the thermal NO because of its high specific heat.