The most common spray break-up models for fuel atomization are presented and discussed. Different breakup models show different spray characteristics and none of the presented models can explain the phenomena observed in several recent works. Up to now there is no confirmation for one of them. Here, a light sheet technique was used to investigate the spray structures close to the nozzle orifice by means of a new detection optics. The experimental results show a liquid jet which is dispersed with cavitation bubbles especially at the edge of the jet. The bubbles implode next to the orifice and create strong disturbances which are increased by aerodynamic interactions. Based on these observation a new idea of a break-up model has been developed. Additionally the two-phase flow was used to determine the flow velocity close to the nozzle.