Hydrogen Traction System in Railway

On September 16, 2018, in the Lower Saxony region of Germany, the world's first two hydrogen-powered passenger trains went into commercial service. These trains are the Coradia iLint developed by Alstom. In February 2020, after more than 180,000 km travelled by these pre-production models, the pilot phase was successfully completed. Several German regions have now confirmed their orders, and by 2023, some 40 iLint trains will be running or in production.

The craze for these trains is driven by the current momentum around hydrogen, an energy vector presented as an essential lever in the energy transition. This momentum is growing worldwide, and all rail manufacturers have embarked on the development of hydrogen-powered trains.

In Europe, hydrogen-powered trains are expected in France, Italy, Austria and the UK by 2025. China, South Korea, Japan and California have also announced their imminent introduction.

Today, two technologies complement each other: hydrogen-powered trains for long-range needs, and battery-powered trains for shorter-range needs connected to power supply infrastructures.

In hydrogen-powered trains, energy is supplied by a hydrogen fuel cell. This converts the chemical energy of hydrogen into electrical energy, releasing only water.

Hydrogen fuel cells cannot operate on their own, and are systematically combined with a current-reversible electrochemical energy source, such as a lithium-ion battery. The latter plays an essential role in supplementing the power of hydrogen fuel cells and reducing hydrogen consumption. A control system is needed to distribute energy judiciously between these two sources.

So, when sizing a hydrogen-powered train, the train builder has to determine the characteristics of each source and the associated energy management strategy. This complex process requires simultaneous consideration of numerous criteria, such as hydrogen consumption, source efficiency and service life, while respecting constraints linked to the train's size and dynamic performance.

Because of hydrogen's characteristics, such as its density, it has to be stored at high pressure (350 bar, for example) to limit the volume of storage systems, and requires specific filling facilities. These stations must adapt to a range of parameters to optimize filling times and limit costs.

The use of hydrogen as a new on-board energy source in trains reduces emissions compared with diesel trains, but leads to greater complexity in on-board architecture and the use of new components whose lifespan has not yet been optimized.

What's more, rising energy costs mean that we need to manage the production...