Flame Characteristics and Pollutant Emissions of a Non-premixed Swirl Burner with Annular Swirling Fuel Injection

Flame stabilization under highly turbulent conditions is commonly achieved using swirling flows in gas turbine applications. The present study investigates the influence of swirling fuel injection on the flame stabilization and emission characteristics of non-premixed and swirl stabilized model gas turbine burner. For the comparative study, three different fuel injection configurations with respect to the swirling airflow (in counterclockwise direction) are chosen-(a) fuel flow unswirled, (b) fuel swirl in clockwise direction, and (c) fuel swirl in counterclockwise direction. The burner is operated with methane fuel and air, for different air nozzle Reynolds numbers 1310, 1970, and 2620 based on the hydraulic mean diameter. The mass flow rate of fuel is varied to get a global equivalence ratio variation from 0.2 to 1.0. In order to compare the structure and flame stabilization location, flame luminosity measurements are carried out. OH* chemiluminescence images are used to estimate the size and shape of heat release zone along with pollutant emission measurements for each case. It is observed that the burner has very low NOx emission at all investigated operating conditions. NOx emission increases with increasing global equivalence ratio. In comparison, case 'b' shows very low NOx emission with respect to the cases 'a' and 'c' for all investigated airflow conditions. Flue gas temperature for case 'b' also has lower values when compared to others. From the flame luminosity and OH* chemiluminescence studies, it is seen that the global equivalence ratio plays an important role in the location of flame stabilization. OH* intensity varies with respect to equivalence ratio for all cases. For case 'a', OH* radical distribution is more spread out and more uniform whereas the others have a localized heat release zone closer to the inner shear layer. Also, the flame standoff distances for the case 'c' are less compared to cases 'a' and 'b'. This indicates fast mixing and high reactivity of fuel-air mixing. In general, for a fixed global equivalence ratio and fuel injection configuration, the change in Re did not have any influence on the flame stabilization location. This demonstrates the high stability of the flames produced in this burner.