**4. Conclusions**

During the design and manufacture of injector nozzles, geometric features are formed that affect the performance. This is accompanied by irreversible pressure losses, which result in energy losses. For ecological and economic reasons, such losses should be minimized. Understanding the influence of geometric features allows to determine their significance and allows to determine their values to minimize pressure and energy losses. Such problems can be solved with the help of built structural and functional models and computer simulations. In addition to geometric features, pressure losses and fuel dosage are affected by the fuel quality and conditions of fuel injection. These studies focused on diesel fueling. Such problems can be solved using the constructed structural and functional models and computer simulation, and experimental tests of the internal combustion engine

conditions and the injection subsystem outside the internal combustion engine. In terms of minimizing pressure losses, the optimal values of the injector nozzle geometrical features assume extreme values for the typical limitations of individual variables. In the case of the spray hole diameter (*drt*), hole surface roughness ( Δ) and spray hole length (*lrt*), the optimal values are the maximum permissible values of these variables. On the other hand, it is the lowest allowable value for the diameter of the inflow channel to the hole ( *Dt*).

Based on the analysis of the variability of the pressure loss function depending on individual variables, it was found that both diameters have the most significant impact on the change Δ *ω*. On the other hand, roughness and the spray hole length on the pressure losses in the injector nozzles are negligible. Therefore, special attention should be paid to maintaining the appropriate dimensions of both diameters in terms of operation. Optimization of injector nozzle geometry of conventional and common rail systems could reduce manufacturing and operating costs and increase system performance significantly.

Further work may concern minimization of pressure losses in front of the injector nozzle, the influence of errors in the shape, friction losses between the needle and the injector body and position of the spray holes on pressure losses and the prediction of changes in the geometry of the nozzles during operation.
