Impact of pilot swirling combination on the flow and emission characteristics of staged lean direct injection combustors

This paper considers a concentric staged triple swirler lean direct injection (LDI) combustor and conducts numerical analysis to investigate the impact of inner and outer swirl flow of the pilot stage on the spray combustion characteristics and NOx emission. To simulate the flow field, spray dispersion, and the combustion process within the combustion chamber Large eddy simulation (LES) is employed. Three geometric dome parameters are studied including the pilot inner swirl angle, pilot outer swirl angle, and pilot flow rotating direction. The results indicate that: (1) The inner swirling flow is the main factor affecting the spray atomization process inside the swirl cup; (2) In downstream of the dump plane, the outer swirling flow determines the evolution of the precessing vortex core (PVC) structures which affect turbulence intensities in the shear layer and efficient spray dispersion, and (3) NOx emissions are related to the spray atomization efficiency and the average flame length in the combustion chamber. It is also shown that NOx emission in the triple swirler LDI combustors is significantly reduced by increasing the swirling intensity and flow rate of the pilot outer swirler.