Several types of twin-fluid atomizers have been developed in the last decades.The mechanism of the liquid primary breakup has been studied in several publications for many types of these atomizers.However,a comparison of the performance of different atomizers is very rare.This study focuses on the examination of four different twin-fluid atomizers.These atomizers are such where fluids are mixed inside the body,i.e.internal-mixing type.The mixing principle differs amongst the examined atomizers.The aim of this paper is to examine the effect of an internal atomizer design to the primary breakup,droplet-air interaction and droplet-droplet interaction in the spray.The phase Doppler analyser(PDA)was used to obtain time-dependent data of the droplet motion.Liquid structures presented in the area near to the atomizer were captured by the high-speed camera.The results point to the differences of the primary breakup even though atomizers were examined under the same operating conditions.Mechanisms of the primary breakup differs for each atomizer.An analysis of droplet velocity were performed for five drop size classes.The velocity profiles confirms the importance of the primary breakup.Two examined atomizers have expected velocity profiles.Other two atomizers differ demonstrably.These profiles were then correlated with droplet collision rate profiles and good agreement was found.Results give an insight into a link between the mixing principle of the atomizer,the primary breakup of liquid and the resulting droplet dynamics.