Fraunhofer Institute for Mechanics of Materials IWM
Fraunhofer Institute for Mechanics of Materials IWM

Characterization of tribological mechanisms and FEM-based wear simulation of thermally high-stressed, exhaust gas-exposed tribological systems for combustion engine operation with hydrogen

Ongoing research project

Current and future climate policy and social goals for CO2 reduction are leading to change in all sectors of the economy and extending into the private sector. There is a shift in thinking about the use of fossil fuels. The currently dominant fossil fuels will be replaced in the future by renewable electricity, hydrogen, and methanized gas. As a result, the requirements for combustion engines will be expanded. In addition to conventional natural gas and diesel, it should also be possible to use H2, H2-methane mixtures, dimethyl ether, methanol, or even ammonia-containing fuels.

The results of IGF project no. 21253 N (topic: Characterization of wear mechanisms in exhaust-exposed, unlubricated tribosystems) have shown the strong influence of the ambient atmosphere on the wear of tribosystems in the exhaust system. These findings are consistent with other publications. However, the effects resulting from the changed exhaust gas compositions when using H2 as an energy source are currently unknown. This poses major challenges for the companies involved, as the design and material selection of the tribological systems in the exhaust system is therefore undefined.

Project description

The main objective of the project is to further develop and verify a qualification strategy for exhaust-exposed, tribologically high-stressed combustion engine components for use in FEM-based wear simulation using sustainable fuels such as hydrogen. The application of this strategy should enable SMEs in particular to cost-effectively characterize materials tribologically, simplify material development, estimate critical geometric changes due to wear during the design phase, and upgrade their components for operation with H2.

First, the understanding of the tribological mechanisms that determine wear is to be extended to combustion engine operation with sustainable fuels such as hydrogen. In this context, exhaust gases containing small amounts of hydrogen with a higher water content and no CO2 are to be expected and will be analyzed experimentally. In addition to established material systems, HT-resistant coatings will be characterized in order to verify the suitability of alternative, sustainable coating processes against the backdrop of a possible Cr-6 ban. Furthermore, FE-based wear simulations are to be developed that enable a quantitative comparison of material behavior and complete the qualification strategy. These simulations allow individual, design-related load scenarios to be considered, thus replacing costly component tests. Furthermore, an online wear database will enable industry partners to build and perform their own simulations based solely on the project results, without having to conduct their own tribological tests. This will make both the material science findings and the methods available to industry partners, enabling targeted optimization of tribosystems and verification of their suitability for hydrogen operation.

Fraunhofer IWM subproject:

The target system will first be analyzed with regard to new fuels. Based on this, three selected material pairings will be systematically characterized tribologically at Fraunhofer IWM in humidified gas atmospheres, as are typical for operation with hydrogen. Fraunhofer IWM's existing tribological test methods will be further developed and adapted to the defined boundary conditions, such as higher water content. At the same time, the mechanisms of action of wear particles will be determined and clearly proven using special experiments.

Once the collaboration with KIT and the in-depth analysis of the tribological mechanisms have sharpened our understanding of the relevant wear processes, various high-temperature-resistant coatings will be tested and evaluated as alternatives to hard chrome plating.

The wealth of experimental results and findings will be used in the further course of the research project as the basis for an FEM-based wear simulation at Fraunhofer IWM. The simulation results will then be validated and evaluated by comparing them with component tests carried out by the industry partners.

Transfer of project results to the following Fraunhofer IWM R&D services for companies:

The project investigates tribological mechanisms in hydrogen combustion engines under high temperatures and exhaust gas influence in order to characterize friction and wear. The necessary testing technology is being specially developed at Fraunhofer IWM and will thus also be available for future research projects. In addition, FEM-based simulations for wear prediction are being developed to optimize the service life of engine components and support SMEs in the development of reliable components for hydrogen engines.

Funding information