Fluid-dynamic and NOx computation in swirl burners

Computational fluid dynamics simulations in a swirl combustor were coupled with chemical equilibrium calculations to evaluate the effects of swirl velocity and burner wall temperature on NOx formation. The fluid-dynamic variables such as velocity, temperature, pressure and species concentrations were obtained by using the finite-element commercial software FIDAP. The chemical equilibrium system under consideration comprised 16 reactions and 20 species. The reaction set included reactions responsible for formation of NOx and reactions believed to be responsible for soot formation in rich fuel–air mixtures. The Newton–Raphson method was used to solve the nonlinear system of equations describing the formation of equilibrium products in fuel–air mixtures. The main goal of this work was to develop a fast and robust computational approach to understand the impact of various design parameters on NOx formation in gas-fired swirl burners. The results showed that increasing swirl monotonically reduced CO and unburned hydrocarbons. The reduction was as high as 5 orders of magnitude. The exit plane NOx did not monotonically decrease with increasing swirl. NOx values initially increased with increasing swirl and then decreased. The procedure outlined in this paper has potential for evaluating new burner designs and operating conditions quickly and robustly.