Spray formation and characteristics for a flash swirl spray were experimentally investigated. To prevent any kind of thermal noise pertinent to the phase change, high frequency dielectric heating method was applied. Laser-based optical technique using Global Sizing Velocimetry (GSV, TSI Inc.) was employed and local droplet sizes were measured on the axial cross-sectional area. In order to obtain the physically meaningful mean droplet size, the time-averaging method was adopted and its Sauter Mean Diameter (SMD) was termed as "total SMD." Experiments involving a total and regional SMD and number percent distributions were conducted at various dimensionless superheat degree, injection pressure, and nozzle diameter. Compared with a cold swirl spray, the sharper decrease in the total SMD of the flash swirl spray with increasing injection pressure is observed. High injection pressure and large nozzle diameter enhance the spray characteristics, including high superheat degree. The presence of the secondary spray observed in the spray core is a unique feature of the flash swirl spray and it contributes to the reduction of the total SMD. (C) 2011 Elsevier Ltd. All rights reserved.