The effects of injection pressure, in-cylinder pressure and in-cylinder temperature at the start of injection on diesel spray penetration were studied experimentally and numerically. The study also considered injection delay, hesitation period and the effect of the number of nozzle holes. The experiments were conducted in a rapid compression machine based on a single cylinder Ricardo Proteus test engine installed at University of Brighton. The numerical studies were carried out using the recently developed multidimensional engine combustion computer code KIVA 3V rel2. Results using single hole, 3-hole and 5-hole nozzles were compared. The injection pressure was varied between 60 and 160 MPa whilst the in-cylinder pressure varied from 2 MPa to 6 MPa. Two in-cylinder temperatures were investigated; 'cold air intake' at 576° K and 'hot air intake' at 721° K. The number of holes within a nozzle was found to have a notable effect on the rate of penetration which was thought to be due to a drop in rail pressure. For the single hole nozzle, hesitation during the initial stages of injection was apparent. This was attributed to the transverse movement of the needle caused by an even pressure distribution round it. As expected, the spray penetration length, for all nozzles tested, increased with increasing the injection pressure and decreased with increasing the in-cylinder pressure. At elevated gas temperatures, a profound reduction in penetration was found due to evaporation during the later stage of injection. A phenomenological model of the break-up length was implemented into the 'KIVA 3V rel2' CFD code. Comparison of the numerical results for liquid tip penetration to those obtained experimentally showed that, the numerical predictions were enhanced when the empirical model for the break-up length was implemented into KIVA 3V rel2 CFD code.