The effect of swirl burner aerodynamics on NOx formation

The problem of pollutant formation in swirling gas flames is a subject of current research at Cardiff University. This paper concentrates on the influence of the levels of swirl on the aerodynamics and NOx emissions at a constant load. Measurements of mean temperature, local velocity and NO−NOx concentrations were taken for swirl numbers from .63 to 3.04. From these a net NOx flow through sections of the flame were calculated. The flames have been classified into 4 broad groups dependent on the influence of the recirculation zone on flame stabilization. These changes in flame type coincide with other changes in the flow structure, as can be seen from the effects on the precessing vortex core. A model based on well stirred and plug flow reactors is proposed for the flows. The results highlight errors in interpretation that can occur by only considering the concentration measurements. In order to establish the source of pollutants in a swirl combustor, it is essential to consider the pollutant mass flow profiles. The formation of NOx in these flows occur in the flame front. The recirculation zone, despite its long residence times and moderate temperatures, does not contribute to NOx formation.