Abstarct: Different breakup models are applied to numerically model a single-hole n-Hexadecane injector, in order to find the most appropriate model for predicting the spray behavior. The simulations are performed in KIVA-4. Spray tip penetration is calculated by use of ETAB, Wave and KHRT breakup models. Results show that ETAB breakup model has better agreement with the experimental results, obtained by HP/HT spray rig of Chalmers University of Technology. As turbulence has an important impact on the droplet collision outcomes, standard k-ε turbulence model and two modified versions of this model are applied to the code in order to calculate the spray tip penetration. It is noticed that these modifications make the results approach to the experimental results. By choosing the most convenient model, the effect of ambient pressure and injection pressure are investigated. Increase in the injection pressure leads to an increase in the penetration length, while increase in ambient pressure shows a reverse effect.