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It is a great challenge to find effective atomizing technology for reducing industrial pollution;the twin-fluid atomizing nozzle has drawn great attention in this field recently.Current studies on twin-fluid nozzles mainly focus on droplet breakup and single droplet characteristics.Research relating to the influences of structural parameters on the droplet diameter characteristics in the flow field is scarcely available.In this paper,the influence of a self-excited vibrating cavity structure on droplet diameter characteristics was investigated.Twin-fluid atomizing tests were performed by a self-built open atomizing test bench,which was based on a phase Doppler particle analyzer (PDPA).The atomizing flow field of the twin-fluid nozzle with a self-excited vibrating cavity and its absence were tested and analyzed.Then the atomizing flow field of the twin-fluid nozzle with different self-excited vibrating cavity structures was investigated.The experimental results show that the structural parameters of the self-excited vibrating cavity had a great effect on the breakup of large droplets.The Sauter mean diameter (SMD) increased with the increase of orifice diameter or orifice depth.Moreover,a smaller orifice diameter or orifice depth was beneficial to enhancing the turbulence around the outlet of nozzle and decreasing the SMD.The atomizing performance was better when the orifice diameter was 2.0 mm or the orifice depth was 1.5 mm.Furthermore,the SMD increased first and then decreased with the increase of the distance between the nozzle outlet and self-excited vibrating cavity,and the SMD of more than half the atomizing flow field was under 35 μm when the distance was 5.0 mm.In addition,with the increase of axial and radial distance from the nozzle outlet,the SMD and arithmetic mean diameter (AMD) tend to increase.The research results provide some design parameters for the twin-fluid nozzle,and the experimental results could serve as a beneficial supplement to the twin-fluid nozzle study.