A twin fluid atomizer of an internal mixing type (TFA-IM) is an atomizer which disintegrates liquids after mixing the liquid with gas and spouts out them from the atomizer port. An atomizer of this type is widely used for atomization of a coal slurry fuel and a viscid liquid fuel. Using immersion liquid method, it was found ex-perimentally that the Sauter mean diameter of a TFA-IM spray along its axis decreases toward down stream. Aiming to make clarify an atomization mechanism by TFA-IM, the mean velocity and the turbulent characteristics of air within the spray and the air jet were measured using LDV. Jets from a nozzle of circular long tube were also examined for a comparison with a jet from the TFA-IM. As the results, it was found that air jets from the TFA-IM have stronger turbulent intensities than these in the jet from the circu-lar long tube nozzle just after its exit and self-preserving of the velocity distribution and the turbulent fluctuation were held within the air jets just spouted out from the TFA-IM. It was also found that these tendencies were held within the spray jets from the TFA-IM. From the relation between decrement tendency of the air turbulence within the spray and decrement of Sauter mean diameter of droplets along the axis of the spray, it was considered that disintegration of liquid, along the spray jet from the exit port of the TFA-IM towards the downstream, may proceeds by the shearing force of Reynold's stress of the air which comes from the strong turbulence of the air within a spray jet.
