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The effect of the working fluid flow conditions and nozzle geometry on the spray performance of a twin-fluid nozzle used in Selective Catalytic Reduction is investigated experimentally. The liquid pressure is varied in the range of 0.3atm to 1.5atm and the air pressure is varied from the 0.5atm to 3.0atm. Relative position between liquid nozzle(internal nozzle) and air nozzle(external nozzle) tip changes from 1mm inside the air nozzle to 1mm outside the air nozzle. The orifice diameter of the air nozzle is varied with 5mm, 6mm and 7mm. Spray visualization is realized with CCD-Camera. SMD(Sauter Mean Diameter) and mean particle velocities are measured by PDPA(Phase Doppler Particle Analyzer) under various experimental conditions. The measuring point is 300mm away from the nozzle tip in the downstream spray. The experimental results are that spray angle is depended air flow rate because nozzle diameter, air pressure and nozzle tip relative positions are related airflow rate. SMD is depended air flow rate and water flow rate. Also, SMD is increased when water flow rate is bigger. SMD is decreased when air flow rate is bigger.