Discharge coefficients, droplet diameters, and droplet velocities for plain-orifice effervescent atomizers are reported for a wide range of air/liquid (fuel oil) ratios. Liquid conditions comprise temperatures of 303 K(30 degreesC) and 353 K(80 degreesC) with corresponding kinematic viscosities of 200 and 24 mm(2)/s. Two different discharge orifices have been investigated with large length/ diameter design ratios of 2.0 and 2.5. Two aerators have been employed with each discharge orifice; these combinations provide ratios of discharge orifice area to that of the total aerator injection holes which varied from 0.0267 up to 0.1157 The measured Sauter mean diameter variations with air-to-liquid ratio confirm the existence of a single "knee" in the profile for the two discharge orifices with length-to-diameter ratios of 2.0. The corresponding profiles for the two orifices with a length-to-diameter ratio of 2.5 show the existence of a double "knee." The results show that previously published correlations for the discharge coefficient are not universal and that contrary to previous observations, the liquid viscosity does have a significant influence on both the quality of atomization and the detailed structure of the spray field.