A numerical investigation is presented assessing the effects of hydrogen compositions and nonflammable diluent mixtures on the combustion and NO emission characteristics of syngas nonpremixed flames for a bluff-body burner. An assessment of turbulent nonpremixed modeling techniques is presented and is compared with the experiments of Correa and Gulati (1992, “Measurements and Modeling of a Bluff Body Stabilized Flame,” Combust. Flame, 89(2), pp. 195–213). The realizable k–ε and the Reynolds stress (RSM) turbulence models were found to perform the best. As a result, increased hydrogen content caused the radial velocity and strain rate to decrease, which was important for mixing whereby NO production decreased. Also, the effectiveness of nonflammable diluent mixtures of N2, CO2, and H2O was characterized in terms of the ability to reduce NO emission in syngas nonpremixed flames. Results indicated that CO2 was the most effective diluent to reduce NO emission and H2O was more effective than N2. CO2 produced low levels of OH radical, which made CO2 the most effective diluent. Although H2O increased OH radicals, it was still effective to reduce thermal NO because of its high specific heat. It will be numerically shown that hydrogen concentration in the H2/CO/N2 flame does not significantly affect temperature but dramatically decreases NO emission, which is important for industrial applications that can use hydrogen in syngas flames.
Stability Characteristics of a Turbulent Nonpremixed Conical Bluff Body Flame
