To study the effect of main swirl number on the flow and combustion characteristics of three-stage swirl combustor

two different main swirl number swirlers were designed. The flow field and flame structure were obtained with particle image velocimetry (PIV) and flame spontaneous emission. Results showed that the change of main swirl number had a great influence on the outlet flow

the lean ignition fuel air ratio and the lean blowout fuel-air ratio. With the increase of the main swirl number

the position of the vortex core was close to the center and upstream location. The height of the center toroidal recirculation zone was increased

while the vorticity of the outflow was decreased. The recirculation velocity and turbulence intensity inside the center toroidal recirculation zone were increased

and the flame structure was symmetrical. The successful ignition time was reduced. Compared with primary stage swirl number 0.7

the lean ignition fuel-air ratio of primary stage swirl number 0.8 was increased by 48%

41%

26%

and 24% at volume flow rate of 200

250

300，350 m3/h

respectively. Besides

the lean blowout fuel air ratio was increased by more than 30% in each operating condition. During the combustion process

the flame burned outward at a certain “V” opening angle. During the ignition process

the flame developed to the inner side along the boundary of the center toroidal recirculation zone.