Influence of high H₂O in hydrogen ICE exhaust atmospheres on cast iron manifold materials: comparative engine and laboratory study

Hydrogen internal combustion engines (H2ICE) represent a promising solution for reducing emissions in heavy‑duty transportation. However, the shift from conventional diesel fuel to hydrogen significantly increases the water vapour content of the exhaust, potentially altering high‑temperature oxidation behaviour of exhaust components. This thesis investigates the influence of high-water-vapour exhaust atmospheres on the corrosion performance of Si‑Mo cast iron manifold materials. Both engine and laboratory tests were performed. In engine tests, SiMo51 exhaust manifolds were exposed for 500 h under real diesel and H2ICE operating conditions, followed by analysis of the scale morphology at different manifold locations representing varying temperature regimes. Laboratory exposures were conducted on SiMo51, SiMo1000, and as‑cast SiMo51 using atmospheres mimicking both a diesel and a H2ICE exhaust. Oxidation kinetics were evaluated via mass‑gain measurements in accordance with ISO 21608:2012, supported by optical and electron microscopy and EDXS analysis of the scale’s morphology. Results reveal clear differences in oxide scale morphology and growth behaviour between diesel and H2ICE environments. The H2ICE atmosphere promoted more uniform and adherent oxide scales, whereas diesel exposure showed tendencies toward oxide delamination and cracking in certain zones. The hottest manifold regions exhibited the most significant morphological differences. The simulated environments enabled assessment of the effects of both water vapour and temperature. Higher water vapour concentrations led to the formation of denser and more adherent Si‑rich (SiMo51) or Al‑rich (SiMo1000) oxide layers at the metal-oxide interface, reducing oxidation rates. Increasing the temperature from 700 to 800°C further densified these layers, lowering oxidation rates by up to an order of magnitude compared to simulated diesel conditions. These findings highlight the role of water vapour in high‑temperature oxidation and provide insight into material performance and selection for hydrogen combustion exhaust systems. This work has been done within the FFI H2MATICE project in collaboration with Traton, Volvo, Ovako and Bulten Group.