Abstract:

PIV technique（particle image velocimetry）is utilized to measure the instantaneous velocity fields in swirling pulverized coal nonpremixed combustion under different staged air injections. The influence of turbulent coherent structure on combustion characteristics and NO formation is studied.Near the inlet of the combustor，larger secondary air ratio leads to early spread of coherent structures and entrainment of small pulverized coal particles into these structures，therefore，the central gas temperature is higher;smaller secondary air ratio makes more big particles move to the vicinity of the wall under the effect of inertial centrifugal forces，resulting in higher gas temperature near wall.In this experiment，larger secondary air ratio contributes to the formation of longitudinal vortices in shear layers and transverse vortices in the field，combustion of small particles and volatilization of big particles，and initially enhances the NO formation，but subsequently stimulates the reaction of NO reduction by intermediate products，and finally slightly decreases the NO concentration.