A 76mm diameter combustor with counter-rotating axial flat 8 bladed swirlers of 45º vane angle was investigated at a reference Mach number of 0.05 or combustion intensity of 20MW/(m²bar), which represents all the combustion air passing through the swirler for a gas turbine combustor application. However, similar heat release rates apply for process burners with a similar pressure loss of around 2% or 20mb windbox pressure. The counter-rotating swirler was very large relative to the combustor so that they had the required high air flow capacity. The inner swirler was 34mm diameter and the outer had an ID of 50.5mm and OD of 76mm and there was no outer expansion. The influence of an outer shroud of 50.5mm dia. was also investigated as this would promote an outer flow expansion shear layer, which was found for single axial swirlers to be beneficial to premixed flame development. The premixed flame weak extinction at 600K was 0.45 Ø without the restriction ring and 0.47 with the restriction ring. Thus the addition of an outer expansion did not improve the weak extinction. This counter-rotating axial swirler was compared with single axial swirlers of the same flow capacity. The flame stability with counter swirl was inferior to that of single axial swirlers where a 45º swirler had a weak extinction at 600K of 0.41Ø. The minimum NOx at 15% oxygen for premixed counter swirl combustion at 1750K with 600K inlet temperature was 2.5 ppm at 15% oxygen for the unshrouded swirler and 5 ppm for shrouded swirlers. However, there was no NOx advantage of premixed counter-rotating axial swirl as a single 45º axial swirler with small hub and the largest outer swirl flow expansion had NOx emissions at 1750K of 2ppm at 15% oxygen. It was concluded that under these severe test conditions of Mref =0.05 there was no flame stability or NOx benefit of using counter-rotating axial swirlers compared with single direction axial swirlers.
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)