**1. Introduction**

Modern diesel engines are the main mobile energy sources, are widely used as stationary power plants, and are distinguished by a high degree of design, working, and technological processes.

The advantages of diesel engines are determined by the high level of fuel efficiency and reliability due to the high level of workflow, all systems, and components refining. But this does not mean that all reserves for further improvement of diesel engine performance have been exhausted.

The main disadvantages of diesel engines include the consumption of natural organic fuels and the contribution to environmental pollution.

Taking into account, the prospects for increasing energy potential in stationary, and especially in transport energy, limited natural resources, deterioration of the environment, today it seems relevant to solve the following problems:


The solution of these problems seems to be a much more rational direction, in comparison with the proposed solutions for the reduction and possible abandonment of the use of diesel engines in the future, which will invariably lead to the energy crisis, which may turn out to be much more painful for humanity in comparison with the ecological one.

In this chapter of the monograph, in order to systematize, select directions, and search for rational ways to improve the efficiency of diesel engines, the main results of fundamental and applied research carried out in recent years at the Department of Internal Combustion Engines of the National Technical University "KhPI" are considered. The experience of the authors in improving the quality of processes in cylinders of diesel engines, in increasing the reliability of the most loaded parts, in ensuring a reduction in the level of emissions of toxic substances and carbon dioxide, including the use of alternative fuels, is generalized.

It is proposed to evaluate the effectiveness of technical solutions to reduce the operating fuel consumption of transport diesel engines and emissions of toxic substances with exhaust gases, use of alternative and hybrid fuels, which includes green hydrogen, is proposed to be carried out using the fuel-ecological criterion. It is shown that further improvement of this criterion is associated with taking into account the impact of carbon dioxide emissions on the environment.

At the same time, the heat generated by the combustion of fuel in the engine cylinders cannot be completely converted into useful mechanical work. To study the efficiency of thermodynamic processes of diesel engines, it is proposed to use the anergy-energetic method of analysis, and the quality of heat conversion into work is estimated by the exergy efficiency, which makes it possible to identify the mechanisms of formation of internal and external losses and substantiate the ways to achieve optimal heat use.

Along with the improvement of economic and environmental indicators and the technical level, the improvement of diesel engines is associated with an increase in liter power, which requires ensuring reliability, first of all, the most heat-stressed engine parts and using modern industry 4.0 technologies.
