The multidimensional simulation methods, today available for spray motion predictions, solve the spray equations including the mass, momentum and energy changes due to the interaction between the drops and the gas, considering also the collision and coalescence phenomena.As concerns break up, two models are the most commonly used: the TAB one, proposed by O'Rourke and Amsden and based on the Taylor analogy, and the WAVE model; developed by Reitz and Diwakar. Both models need the tuning of some empirical constants.Considering also that the mechanism, that controls atomisation, is not yet well understood, it seems that further calculations and experimental comparisons over a range of injection conditions may be useful to improve the prediction capability of these models.Therefore the present paper concerns a sensitivity analysis of the TAB and WAVE models to changes of the empirical constants.The high speed photography and light extinction techniques were adopted to characterise the spray behaviour in terms of liquid tip penetration and Sauter Mean Radius. Measurements for comparisons were carried out m a real direct injection (D.I.) diesel engine equipped with two small optical accesses and two endoscopes.Finally, in order to improve the numerical predictions, a ‘hybrid’ model is proposed, based on both the TAB and WAVE models. The corresponding tests and results are given.