This paper investigates the injection of fuel into a constant volume spray chamber at high pressures by utilizing macroscopic fuel spray characteristics of mineral diesel and rapeseed oil biodiesel. In the case of lower spray chamber pressure the shapes of fuel sprays tend to be more inclined and indicate higher cavitation inside the nozzle hole. On this basis and from experimentally obtained spray tip penetration and spray angle, a modified mathematical model for spray tip penetration and spray angle is developed. This new model includes two-zone theory and the obtained results agree very well with experiments through the whole interval of spray development.