Despite the initial aim of “phasing out” the combustion engine, the industry has retained a certain openness to technology, especially as the combustion engine has an intact (further) development, production and operating infrastructure. The combustion engine will remain the most widely used drive system for many years to come, particularly in heavy commercial vehicles and in the off-highway sector. The market share of alternative fuels or blends on a biogenic and synthetic basis will increase and make an important contribution to climate protection. Many studies to date have focused on the thermodynamic side of the combustion process. The subject of this study is the influence of alternative fuels and their decomposition products on the durability and stability of the materials used in the fuel circuit of seals, plastics and filter media. The influence of gaseous fuels such as hydrogen on the lubricating oil circuit is greater than is usually expected. The materials can be validated using suitable test methods. Suitable filter systems and separators help to reduce wear on the combustion engine and the sensitive injection system.