**Abstract**

In this chapter, we investigated the effect of geometric parameters of the nozzle orifice on cavitating flow and entropy production in a diesel injector. Firstly, we analyzed the effect of some parameters of diesel injector such as the nozzle length and the lip rounding on cavitating flow. In the second parts, we studied the entropy production inside the diesel injector in several cases: -single phase and laminar flow,- single phase and turbulent flow and –tubulent cavitating flow. In the last case, the mixture model cupled with k-ε turbulent model has been adopted. The effects of average inlet velocity and cavitation number on entropy production have been presented and discussed. The results obtained show that the discharge coefficient is weakly influenced by the length of the orifice and the radius of the wedge has a large effect on the intensity and distribution of cavitation along the injection nozzle. On the other hand, the study of entropy production inside the diesel injector shows that the entropy production is important near the wall and increases whith increasing the average inlet velocity and pressure injection.

**Keywords:** Cavitation, Diesel injector, Entropy generation, Simulation, Mixture model
