One of the biggest challenges of modern aviation is the development of technologies that reduce or eliminate emissions of harmful combustion components into the atmosphere. European authorities are imposing increasingly stringent emissions regulations. Therefore, new models of combustion chambers, new combustion methods, as well as new types of aviation fuels must be developed. This article presents the possibilities of using hydrogen propulsion in aviation. The reasons for conducting research on hydrogen propulsion are discussed, as well as the history of the introduction of hydrogen propulsion into aircraft engines. Problems that can be encountered in the production and storage of hydrogen are identified and explained. Proposals for the use of hydrogen combustion or the use of fuel cells to power turbine engines are also presented, and the economic aspect of this type of fuel is discussed.

In the present study, using a combination of theoretical discussions, practical examples, and case studies, we sought to gain a comprehensive understanding of how numerical solutions could be used to improve the design and optimize the thermal efficiency of a heat exchanger that utilizes wastewater to reduce the domestic consumption of hot water. To this end, we developed a validated numerical model. We also carried out simulations and experiments, the results of which are presented in this paper. The novelty of this work derives from our use of a new heat exchanger design for a domestic shower, and from the presented experimental–numerical evidence that proves its efficiency. We found that use of our newly designed appliance improved thermal efficiency from 14% to 27%. Moreover, we estimated that the cost of manufacturing and installing such a device did not exceed that of a widely available drain grid. Using our newly designed exchanger, a family of four living in Poland could save EUR 38 (at 2022 values) and reduce CO₂ emissions by 192 kg. An average European family could save EUR 68 and reduce CO₂ emissions by 76 kg.

The improvement of unleaded fuels in general aviation represents a significant milestone in the pursuit of establishing a greener and more sustainable air transportation system. Conventional aviation fuels, such as AVGAS 100LL, have TEL (Tetraethyl Lead) in their composition, which is used to increase the octane rating of fuel and improve the efficiency of piston engines used in aviation. However, these substances are considered toxic, and their emissions into the atmosphere have negative effects on the environment and human health. Therefore, very strict air quality standards have been established by the European Union and member states. Years of research and cooperation throughout the aviation sector have contributed to the elimination of lead-containing fuels from most aircraft used in general aviation operations. Most engines have already been certified for the usage of unleaded gasoline, and so are all new engines. Nevertheless, one-third of the engines currently in use in the EU are not certified to burn unleaded fuel. Besides the lead, other toxic compounds are also being emitted with exhaust gases like CO2, NOx, and UHC. In this article, the discussion is about the profits of pursuing a zero-lead policy within General Aviation and the risks associated with introducing a leaded avgas prohibition without a valid alternative.