New freight propulsion concepts a ‘technological awakening’ for rail freight

Rail freight has a critical role to play, both in terms of European competitiveness and in meeting the ambitious climate objectives set out in the Green Deal. In fact, the Sustainable and Smart Mobility Strategy (SSMS), the European Commission guidelines for transport policy, specifically states that transport must become more sustainable, intelligent and resilient. To achieve this, the Green Deal, together with the SSMS, set the ambitious goals of a 90% reduction in transport emissions by 2050 and an increase in rail freight of 50% by 2030 and doubling it by 2050.

Delivering these targets first requires rail freight to be positioned as a cost-effective and attractive service option to shippers. However, the challenge is that today’s rail freight transport is a complex activity that, as a result, can be slow, heavy, and unreliable. In other words, rail freight is need of a rapid transformation.

Which is exactly what Europe’s Rail set out to do.

Improving the overall performance of freight locomotives

With the aim of initiating a ‘technological awakening’ for rail freight transport, the initiative conducted a number of technical demonstrators (TD). Through automation, digitalisation, interoperability, energy efficiency, innovation, and infrastructure, these TDs look to make rail freight a more attractive and sustainable transport option.

One of those Technical Demonstrators investigated new freight propulsion concepts. Specifically, it looked at how the addition of different technologies for flexibility, hybrid operation, remote control, and automation could enhance locomotive performance, operational efficiency, and cost-effectiveness. It also looked at a freight locomotive’s various operational modes, which encompass such activities as track service, shunting, and last-mile operations.

Based on this research, the TD delivered three categories of future freight propulsion systems.

1. Multimodal energy supply and energy storage unit (ESU) development

TRL 4 (technology validated in lab)

The multi-system freight locomotive of the future will feature an (optional) energy storage system (ESS), along with a second set of locomotives for catenary-free operation (CFO). The latter will include an ESU that will improve overall efficiency, reduce costs, and decrease emissions.

ESU vs EES

The energy storage system (ESS) encompasses the whole system, including the electronics storage unit (ESU), power electronics, control, cooling, etc. The ESU, on the other hand, holds the actual energy storage (battery, hydrogen power cell, etc.) plus the ESU’s cooling system.

Ultimately, such a locomotive architecture will enable door-to-door freight service without having to change the locomotive.

Discussion and key findings

• Within the ‘last mile’ concept, the ESU, which is based on mass production cells or modules, requires an ESS to supply electric energy to the locomotive’s main circuit. Such an ESS will be comprised of some kind of energy storage and energy supply/control unit.

• ESS will enable CO2 free operations in environments where catenary systems are not available yet are very important for rail freight (some yards and terminals do not have catenary systems). This will enable the opening of new routes to electric locos, reducing the need of diesel shunting locos.
• The use of Silicon Carbide (SiC) technology also delivers better energy performance (up to 2%).
• As a technological component for the battery-based ESU, the TD developed a laboratory-tested conceptual design that puts lithium-ion cells into stacks of 400 cells, with each stack connected to form a series. To facilitate maintenance, the cells are grouped into modules. The configuration of the final ESU would consist of 400 cells in a series across each of the 30 parallel modules.
• The mission manager is key to the CFO completing the mission with the available energy and within an acceptable time. Optimal target speed curve can be calculated using the input of the track altitude and speed limit profile, together with the train and locomotive parameters. The advantage offered by this solution is the rational management of energy demand during high-demand scenarios (e.g. train start-up, passing through voltage change zones).
• Battery management is crucial, not only for delivering additional energy during peak demand, but also for storing energy during braking. Integrating battery management within the traction chain mitigates any local demands that would otherwise be absorbed by the locomotive, thus enhancing the energy efficiency of both the locomotive and infrastructure.

2. Concepts for traction/auxiliary systems based on SiC technology

TRL 4 (technology validated in lab)

According to TD research, SiC MOSFETs can reduce energy waste – making trains more efficient and cost-effective. More specifically, switching from traditional silicon (Si) semiconductors to a SiC metal-oxide-semiconductor field-effect transistor (MOSFET) delivers better energy performance (2% improvement) that, when taken into the whole life cycle of the asset (min. 20 years), results in a major figure in energy savings. It also reduces the size and weight (expected around 20%) of the necessary on-board power converters, freeing this capacity to offer better traction profiles.

Discussion and key findings

• According to a simulation study conducted by the TD, future freight locomotives will likely use SiC-based traction converter modules and optimised components to work with SiC. Such changes could decrease energy consumption by as much as 2% per year (in typical European operating conditions).
• By saving space and weight, medium frequency (MF) auxiliary power supply (APS) designs make way for more features, extra energy storage, and the electronic systems needed for advanced train operations. Based on current costs, switching to MF APS becomes cost-effective after 20 to 30 years of using the vehicle. With potential annual energy savings of up to 22,000 kWh per 100 km, the benefits of MF APS outweigh the initial investment over the locomotive’s lifetime.

3. Distributed power system (DPS)

By making operations more reliable and safer, the use of DPS opens the door to using longer freight trains. However, this requires a DPS architecture that removes all wired train-line connections between traction units and that does not restrict the position of the locomotives within the train consist (although network restrictions must be considered).

DPS in detail

DPS needs command and control for applying power/traction and coordinating the braking. This can be done by means of cabling (Traditional Wired Train Bus) or via radio. However, using a cable-based solution can cause issues with the freight train formation (all wagons must be cabled and tested once the convoy is set) unless DAC technology is used.

Discussion and key findings

• DPS is an enabler for long trains (traction for 750 m trains can be a challenge depending on the gradient of the route) and enables ‘last mile’ rail operation or platooning (e.g. convoys departing from one origin that split at a given point to reach its destination, normally big industrial customers with freight rail terminal).
• The key is to ensure that the DPS architecture is centred around managing available traction power in the train. This means utilising transmission mechanisms that interconnect traction components within a communication-based management system. This setup enables the operation of longer trains.
• The DPS architecture uses three independent communication channels:
  • Brake pipe (or pneumatic channel): crucial for transmitting commands via pressure changes and supplying brake energy across all trains (including DPS).
  • Data bus (or wired channel): facilitated by the digital automatic coupler (DAC), the data bus integrates all wagons and locomotives in a freight train. This enables direct access to the train communication master from the lead locomotive.
  • Radio-based communication (or wireless channel): although currently optional, in the future this will be supplemented by the DAC system and its wired network. There are also long-term plans for establishing wired communications as the primary data pathway and wireless as a backup.

This TD was successfully taken up to TRL 7 (system prototype demonstration in operational environment) with three locomotives under DPS in a 350 m heavy convoy during several runs under different gradients.

Advanced functional features and new performance specifications

What the TD’s research and findings make clear is that the future freight locomotive will include several advanced functional features and performance specifications.

The future freight locomotive

The advanced functional features and performance specs of the future freight locomotive.

While the features and specs may change, the freight locomotive itself will maintain a similar basic layout and tractive performance as current models – thus answering the demand for hauling longer trains by adding and integrating new functions and technologies to legacy locomotives (e.g. DPS) instead of the more costly development of a new freight locomotive.

The prospective operational modes of the future freight locomotive present numerous benefits for railway operators. For example, daily procedures involving the freight locomotive, such as train inauguration and maintenance, all stand to benefit from enhancements, increased speed, and simplified processes.

In summary

New freight propulsion concepts can improve the overall performance of today’s locomotives by adding and integrating additional functionalities and technologies. This will provide extreme flexibility for operation in non-electrified and electrified lines and enable remote control for distributed power. It will also increase operational efficiency by automating such activities as train start-up, train preparation, start of mission, stabling, parking, and shunting.