**1. Introduction**

The fuel injection process is the primary action influencing the reach of the desired parameters of the compression ignition engine cycle. The formation of the fuel stream and its disintegration during spraying, and then the formation of the fuel -air mixture depends on the physical properties of the fuel, the pumping pressure and the opening of the injector, air swirl, as well as the advanced design of the injector nozzle and the quality of workmanship [1–4].

Incorrect operation of injection equipment in compression-ignition engines, caused by imperfect workmanship and wear, significantly affects the engine performance, increased fuel consumption, toxic emission and smoke opacity of outlet gases. The research conducted so far has shown that the injector is the most unreliable element of the injection subsystem, and the nozzle in the injector [5]. Changes in its technical state significantly affect the engine operating parameters and the emission of harmful components of the outlet gases [6,7]. The injector nozzles work in very rugged conditions, with high pressures of the fuel and the working medium in the engine's combustion chamber, and with the simultaneous interaction of the heat flux with flames and outlet gases [8].

 Monieta, J.; Kasyk, Optimization of Design and Technology of Injector Nozzles in Terms of Minimizing Energy Losses on Friction in Compression Ignition Engines. *Appl. Sci.* **2021**, *11*, 7341. https://doi.org/10.3390/app11167341

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**Citation:**

Academic Editors: Cinzia Tornatore and Luca Marchitto

Received: 10 June 2021 Accepted: 5 August 2021 Published: 10 August 2021

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These are elements with a complex structure, high precision of workmanship and the required high durability. The introduced design changes and modernization of the engines produced require the improvement of the manufacturing technologies used. The purpose of these changes is to increase the maximum combustion pressure and mean effective pressure, reduce specific fuel consumption and increase durability and reliability.

The requirements for injector nozzles can be divided into design and technological. Design requirements are related to the functions, operation of the injector nozzle, durability and reliability, as well as interchangeability and standardization. Technological requirements, which determine the quality and cost of execution, include the possibility of obtaining high dimensional accuracy and surface smoothness as well as small errors in shape and position.

Studies have shown that many injectors are damaged in the initial period of operation [5,9]. The reason for such a situation may be the initial unfitness or low durability, which may result from the conditions of production, transport and storage [2,10]. The analysis of the quality control requirements of the manufactured injectors has shown that they are not very credible and not uniform. The modern state of the technology of producing nozzles does not ensure their hydrodynamic similarity because the dispersion of their geometrical dimensions is difficult to determine by means of industrial quality control methods [2,9].

One of the design dimensions of nozzles, determining their technical state, and at the same time subject to intensive wear, are the geometric features of the spray hole [9,11–15]. Changing the dimensions and condition of the spray hole surface significantly affects the flow properties of injector nozzles, and this, in turn, determines the size and form of fuel jets dosed to individual cylinders of a diesel engine and the quality of fuel atomization. Many investigations have shown that the nozzle hole geometry and its internal flow characteristics play an essential role in the spray formation [2,12,16,17] and combustion process [7,8,14,18].

This article intends to present a simulation model of the injector nozzle structure of a marine engine, which is part of the fuel injection subsystem. The main task is to develop a modern model, considering the latest theoretical and numerical achievements, of a marine engine injector nozzle. In the current article, it is expected that the method of optimizing the design of the injector nozzles will contribute to the reduction of fuel flow losses and the improvement of the efficiency of the piston internal combustion engines.

The injection subsystem tests can be carried out on a real object in operation [5], on a real object in laboratory conditions [9,10] and with the use of computer simulation [19,20]. The essence of simulation studies of the fuel injection process is developing models that allow understanding the physical phenomena that determine the quality of injection.

#### **2. Modeling and Experimental Studies of the Geometry of Injector Nozzles**
