THE pressure-swirl atomizer, sometimes referred to as a simplex atomizer, is widely used for liquid fuel injection and combustion in rocket engines. The pressure-swirl atomizer ensures highperformance atomization and has a wide stability margin range during operation, especially for the injectors used in rocket engines. The discharge coefficient, spray angle, and film thickness are the main atomization characteristics of the pressure-swirl atomizer. As the discharge coefficient increases with increasing atomizer constant K, the liquid film thickness also increases, while the spray angle decreases. Using the discharge coefficient, the spray angle and the liquid film thickness can be readily estimated to provide key information on the characteristics of liquid droplets. Bazarov et al.[1] derived an equation to obtain the spray angle from the actual discharge coefficient. Kim et al.[2] and Fu et al.[3] recently introduced empirical equations to predict the liquid film thickness by directly calculating the mass flow rate from the discharge coefficient. In the past, a considerable amount of progress has been made in characterizing the discharge coefficients of pressure-swirl atomizers [4, 5]. Extensive experimental diagnostics have been conducted to develop empirical equations for a broad range of conditions. However, the swirl atomizerflow characteristics require further study to ensure accurate predictions of the discharge coefficients. Accurate atomizer discharge coefficient estimations are important in the early design stage of liquid rocket engines because the atomizer pressure drop affects the pressure budget of the other subsystems. Moreover, atomizers with low nozzle opening coefficients are generally preferred given the available installation space in the combustion chamber manifold. Therefore, accurately predicting the discharge coefficient of atomizers with low nozzle opening coefficients is indispensable to the design of atomizers. However, for developing this type of atomizer, the previous empirical equations have poorly predicted the discharge coefficients of atomizers with low nozzle opening coefficients. Therefore, a more reliable empirical equation is required for atomizer development. In this study, 44 pressure-swirl atomizer configurations with a wide range of nozzle opening coefficients were experimentally studied. This article is organized as follows. First, several existing empirical models are discussed and summarized. The experimental method is then briefly described, followed by the presentation of the newly derived, empirical equation for predicting the discharge coefficient.