This study presents a droplet collision model which takes into account trajectories of colliding droplets. Droplet collision dynamics can be represented more realistically by using a trajectory based model since collisions are calculated by the position and velocity vectors of droplets. Unlike the O'Rourke's model which is used in KIVA code, the presented model is not mesh dependent. The key point of the model is defining the droplet impact parameter. In this study, a new calculation method of impact parameter, which is based on binary droplet collision model, is presented. The impact parameter of two colliding droplet is obtained by following their colliding trajectory. The algorithm was implemented into the KIVA3V Rel2 code and obtained droplet calculations were compared with O'Rourke's collision model. Binary collision of droplet pairs were taken into account and the impact parameter of two colliding droplets was calculated from their position and velocity vectors. The new model represents the physical process of collusion more accurately since it uses colliding droplets in the calculations. (C) 2012 Elsevier Ltd. All rights reserved.