## 1 Introduction  
Diesel engines are still the main source of power for construction machines, ships, agricultural machines, etc., because of their higher fuel efficiency and greater output power compared to gasoline engines. However, the emissions of diesel engines are still very high, especially particulate matter (PM) and nitrogen oxides (NO\({}_{\text{x}}\)). To reduce the emission content of diesel engines, three main approaches are used. They include a redesign of and improvement in engine structures; installation of exhaust gas recirculation systems [1, 2]; and biofuels and lubricant additives [3, 4, 5, 6]. Emissions of NO\({}_{\text{x}}\) and PM decrease and increase, respectively, if the emission recirculation rate, fuel injection pressure, and turbocharger pressure increase [7, 8]. In addition, exhaust gas treatment on the exhaust pipe with a selective catalytic reduction (SCR) and diesel particulate filter (DPF) systems is a solution often chosen to improve the exhaust gas quality of diesel engines [9, 10, 11]. The enhancement of engine design is associated with an improvement in the fuel system, selection of the combustion chamber geometry, or increase in the boost pressure (\(p_{in}\)). The above solutions can be combined to achieve emissions quantities complying with increasingly stringent ecological standards [8]. The geometric shape of the combustion chamber enhances the rate of turbulent mixing when the piston approaches the top dead center (TDC) [12]. Furthermore, the turbulent movement in the combustion chamber improves the air-fuel mixture, which reduces the time of ignition delay [13]. Improving fuel systems is a basic development trend to perfect diesel engines, especially common rail (CR) fuel injection systems. This research direction includes increasing the injection pressure [14] or ensuring multiple injections [15; 16; 17]. Additionally, controlling fuel distribution in combustion chamber zones or using a lot of fuel are two possible solutions [18; 19]. Pulse duration and pressure are two factors that define the fuel injection process [20]. The fuel injection process is also strongly dependent on the wave phenomenon in the high-pressure pipeline, especially with multiple injections [17; 21; 22]. Studies have demonstrated that the fuel injection process on diesel engines greatly affects the combustion process and diesel engine parameters. Increasing fuel injection pressure needs to be combined with other structural modifications of the injectors, the combustion chamber, and other engine advances that reduce the specific fuel consumption by up to 4% [21]. At the same time, the fuel injection pressure has a direct effect on the vaporization and air-fuel mixing efficiency in the combustion chamber [17; 18; 23]. Under high-load conditions, engine power is related to the penetration rate of the fuel spray and the combustion rate of the fuel-air mixture in the combustion chamber [24; 25]. According to [PERSON] and et al., when increasing the fuel injection pressure from 150 to 240 MPa for large-sized diesel engines, the results show that ignition delays are reduced by 40%, engine efficiency is increased by 4%, and fuel combustion time in the combustion chamber is reduced. In addition, the amount of \(\mathrm{NO_{x}}\) emission at 150 MPa is virtually unchanged [26]. Other studies also show that the amount of soot will decrease when the fuel injection pressure increases and the injector hole diameter decreases [27]. With different nozzle diameters and increasing injection pressure from 100 to 300 MPa, the results present that injection pressure has a small effect on the properties of the mixture, but plays an important role in providing enough energy to fuel vaporization and spray lengths by using micro-hole diameters. The micro-diameter nozzle combined with high pressure is a better combination than conventional nozzles, which increases the rate of vaporization and reduces the time of homogenization of the mixture in the combustion chamber.