Tribological challenges of the cylinder bore in H₂ ICEs

Abstract

Clear messages are coming from the Asian region in particular, both in terms of economic policy and industry, that the internal combustion engine is once again gaining strategic importance in the context of open-technology competition with the fuel cell and battery-electric drive.

So far, the focus on hydrogen combustion has been on combustion process development. Starting from PFI, with relatively low power output, current investigations are moving toward direct injection. Water injection for hydrogen engines is also the subject of discussion, and the first runs on the test bench are being completed. These increasing demands on the tribological system, such as the interaction between pistons and piston rings on the cylinder bore, require intense interaction between a number of disciplines. Corrosion and material compatibility are not the only challenges, but also the washing off of the engine oil, which have to be solved by a carefully targeted choice of materials and optimized honing. In addition to the basic setup, which makes the system durable for its lifetime, the focus is on the 1 g/km CO₂ target. The conflict of goals of low oil consumption with low friction is countered with new approaches to surface finishes. New tooling and software solutions make it possible to qualify the cylinder bore for the tasks of hydrogen combustion without a significant increase in cycle time in series production.

For the piston-group/liner system, an expanded understanding has been built up in recent years, which can now be used in hydrogen engines in combined form.