The rail sector, despite still having one of the lowest carbon footprints in the transport segment, is strongly committed with the world Greenhouse gas (GHG) emission reduction efforts. To do so, there are multiple pathways, with one of the most effective option being the use of renewable hydrogen fuel for propulsion.

Following the rapid and intensive development of alternative traction and fuel technologies in other transport modes, mainly within the heavy duty road sector and the associated technological spillover, the hydrogen fueled internal combustion engines (H2ICE) and the hydrogen fuel cell (H2FC) systems have been set as important technologies to reduce the rail sector environmental footprint.

The H2ICE technology relies on the already mature and commercially available heavy duty internal combustion engine technological platform, which thermochemically converts the fuel energy into thermal energy for power generation. The H2 ICE have no carbon emissions, with just nitrogen oxides (NOx), emitted due to high-temperature hydrogen combustion with air and trace amounts of hydrocarbons (from the lubricating oil). The H2FC technology, in its turn, relies on an electrochemical reaction, in which the molecular hydrogen reacts with oxygen, producing electric energy, as well as water and heat as byproducts.

The main advantages of the H2ICE drivetrains are the reliance on the well proven and mature ICE technology, the great tolerance to fuel impurities and the low use of scarce materials, which ultimately might set them as a carbon-neutral bridging solution towards zero carbon rail powertrains. The H2FC powertrain, on the other hand, besides being an infant technology, also requires minimum levels of hydrogen purity, as well as the use of rare materials (such as the platinum for catalyst). Moreover, it also has inferior durability, compared to the ICE.

Besides the powertrain related topics, both technologies face the hydrogen production and onboard storage challenges, which might be properly addressed to make feasible the transition from fossil (diesel) fuel to hydrogen fueled rail powertrains.

This work, presents a review of the hydrogen fueled rail traction technologies, based on the public available data from technical papers and journals, showing the technology’s current status, as well as the technological required improvement pathways.

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