**5. Conclusions**

The improvement of diesel engines, as the main source of modern energy, is associated with a further increase in fuel efficiency, liter capacity, and reliability, with a significant reduction in emissions of toxic substances and carbon dioxide into the environment.

The proposed systematic approach to a comprehensive assessment of fuel efficiency and emissions toxicity allowed proposing a dimensionless criterion that takes into account the operating conditions of the engine. Using this criterion, an assessment of the efficiency of using alternative fuels is given and the prospect of such an assessment is shown when using hybrid fuels that include green hydrogen.

To identify the mechanisms of the formation of internal and external losses and substantiate the ways to achieve optimal heat use, the use of the anergy-energetic method of analysis is justified.

In order to increase the reliability of the most thermally stressed parts of highly accelerated engines, taking into account the operating conditions, the approach has been proposed, taking into account the complexity of factors affecting the physical and parametric reliability.

The directions for improving diesel engines, considered in the chapter, are only a part of a set of tasks, the solution of which seems to be extremely relevant from the point of view of preventing an energy crisis and, at the same time, are only a part of the possible ones for practical implementation.
