The way is paved for Mireo Plus H

When you listen to Peter Eckert and Nikolaos Papaiordanidis, you can sense their enthusiasm for their shared task of launching Mireo Plus H, the first hydrogen train from Siemens Mobility. Their work on the prototype for testing it under real operating conditions is the culmination of a year’s development that our interviewees helped shape in significant ways. We spoke to them about what really matters in modern trainsets, why this prototype is so interesting, and why it’s also an important part of a larger development.

Mr. Eckert, every prototype is different. What’s special about Mireo Plus H?

Peter Eckert: Our Mireo Plus H is the first prototype that combines the latest hybrid technology consisting of fuel cell and battery with our drive technology in one vehicle, and is also the first to be tested in passenger rail service. Instead of a pantograph, its power supply is a fuel cell that is fed hydrogen from tanks on the roof. It has a battery that delivers traction power and uses regenerative braking. All this is combined with state-of-the-art technology, integrated on one of today’s most modern and lightest-weight trains. The combination of innovative design and the latest sustainable technology is what makes it so special.



Nikolaos Papaiordanidis: It’s the trainset itself, but also an innovation, totally redesigned with a strong focus on sustainability, a high degree of utility for the operator, and extreme comfort for passengers. With this prototype, we’re not only testing interactions between the technical components. We’re also looking at the overall optimized concept of a hydrogen train in combination with an H2 infrastructure. We want to know how it behaves in regional transport. What are the operator’s possibilities for responding to transportation requirements quickly and flexibly? How does the planned hydrogen infrastructure fit into these scenarios? And, of course, we also want to know how well our newly developed technology works in practice.

With this prototype, we’re not only testing interactions between the technical components. We’re also looking at the overall optimized concept of a hydrogen train.
Dipl.-Ing. Peter Eckert, team leader for the development of hydrogen hybrid systems at Siemens Mobility GmbH  

Alternative drive technologies are becoming increasingly important in regional transport. What do you see as the role of Mireo Plus H?

Nikolaos Papaiordanidis: As one of the employees responsible, I naturally see it as having a tremendous role. Our main focus has been on enabling it to meet the current challenges in regional transport on non-electrified routes while anticipating future developments that we can already predict. These primarily involve carbon-neutral mobility. But it’s also much more than that, including classics like low lifecycle costs and high vehicle performance, which enable customers to reduce the intervals between trains or design timetables where the vehicles can be decoupled or routes extended. The regional trains of the future must be able to take advantage of these solutions, in what will have to be a modularly combinable form if they’re to optimally benefit the environment, operators, and passengers. This is exactly what’s behind the Mireo Plus H platform concept, and operation of the prototype will provide us with important insights into how we can best support the various goals of our customers.

Peter Eckert: Let’s take the issue of operating range, which is as applicable to rail as it is to road. As soon as you have to carry traction power on board, you have a limited operating range that depends on the capacity of the tank that can be installed as well as on the weight and size of the batteries. Optimizing the system to achieve the longest possible operating range requires a skillful interaction between the hydrogen and battery systems. But what is usually forgotten is the effect of the basic vehicle on this design and optimization. The Mireo family has been fundamentally redesigned as a two-car and three-car trainset with a view to saving energy – from its many lightweight car shell components to its improved aerodynamics and newly developed traction kit. Based on this energy-saving, modular platform, we’ve optimized a battery-powered train (Mireo Plus B) for up to 120 km distance, and Mireo Plus H as a hydrogen-powered train for ranges of up to 1,000 km – depending, of course, on the mode of operation and line topology.

Nikolaos Papaiordanidis: And both vehicle types have the right vehicle dynamics for increasing the passenger service frequency. With vehicle traction power of over 1 MW and maximum speeds up to 160 km/h, they operate perfectly on main lines without interfering with other traffic.

What makes Mireo Plus H so special as far as its technology is concerned?

Peter Eckert: To put it simply, the next-generation H2 propulsion system. Its wheels are driven directly – meaning without cardan shafts – by converter-fed induction generators. Power is supplied by the high-performance traction battery, which relies on extremely safe, cutting-edge lithium-ion technology and is also designed for regenerative braking. So the traction battery powers Mireo Plus H’s acceleration processes, whereas the hydrogen system charges the battery and supports the on-board power supply during normal operation at a steady speed. The figure shows the main components of the traction system for a two-car Mireo Plus H.






Nikolaos Papaiordanidis: A key element of the modular Mireo Plus concept is the traction kit. Hydrogen-powered and battery-powered trains make use of the same kit, with modules optimized for each. The basic difference is the power supply, which is fed by the fuel cell in the case of Mireo Plus H and by the overhead line in the case of Mireo Plus B. The figure provides an overview of the traction kit components based on the example of a Mireo Plus H vehicle.

What can you tell us about the innovations of the traction kit?

Nikolaos Papaiordanidis: Let’s start with something really unusual. Hydrogen has a special property. When there’s a drop from high pressure (for example, at the filling station) to low pressure (for example, in the empty tank), hydrogen doesn’t cool off like other gases. Instead, it heats up, and the faster the refueling process, the more it heats up. This means you have to make sure that the temperature rise in the tank system is within a permissible range. To keep refueling times as short as possible (comparable to refueling a diesel train), the vehicle’s refueling process is adapted to the infrastructure via various parameters, such as hydrogen precooling. We’re guided by the usual standards for refueling processes, but in light of the overall system comprising vehicle and infrastructure, we also have to reconsider the possibility of an OPEX-optimized refueling process. And this very thing is one of several innovations in our system. The pictures show a tank rack, and the Type IV tanks as individual components.

Peter Eckert: Because of roof-mounting and the limitations in terms of space and weight, a fuel cell with a much higher power density (compared to a conventional system) was developed. The concept includes integration of all the auxiliary equipment, a specific fuel cell stack design, and the controller for the fuel cell system. The stack design, plus an operating mode adapted to the train’s performance characteristics, serve to minimize fuel cell aging to the point where we can now count on a stack service life of around 30,000 operating hours.


Nikolaos Papaiordanidis: We also had to break new ground in the areas of tank systems and H2 piping. The pressure tanks are designed and optimized for operating on the vehicle throughout the entire lifecycle. The tank’s lightweight design as a Type IV pressure vessel helps us reduce the vehicle’s total weight. Process data like the tank system’s pressure and temperature is recorded by the gas handling-unit (GHU). Based on the GHU data, we can see the tank’s filling level, similarly to the way a diesel train’s fuel gauge indicates the filling level of the diesel tank.

Mireo Plus H can also be refueled from either side, which means the train doesn’t have to be turned around. The fuel ports are at a conveniently accessible height in the intercar gangway, near the Jakobs-type bogie. The pipelines were specially developed to meet the requirements of hydrogen applications for tightness, purity, and handling.

A key element of the modular Mireo Plus concept is the traction kit.
Dipl. -Ing. (FH) Nikolaos Papaiordanidis, subproject manager for hybrid propulsion technologies of the Mireo Plus platform at Siemens Mobility GmbH

Regarding the tank, do you have any concerns about safety?

Peter Eckert: We’ve paid particular attention to the hydrogen tank. We use different sized, Type IV pressure cylinders, as already mentioned. The pressure-bearing outer layer of the tank is composed of several layers of carbon fiber that enclose a hydrogen-tight, non-metallic liner as a laminate. The end caps (called BOSS) are made of stainless steel. The result is Type IV tanks arranged in racks of different sizes whose dimensions take full advantage of the roof contour. The piping, the gas control system, and the electrical interface form the end of a tank module. Thanks to the high power density and high refueling speed, hydrogen refueling times are comparable to those of a conventional diesel trainset with a comparable operating range. To shorten refueling times even further, the hydrogen can be precooled in the filling station to prevent an excessive temperature rise. The refueling process is monitored by the filling station and the vehicle. A closed cover protects tanks against UV rays and mechanical damage.


The on-board power electronics also affect energy efficiency. What innovations does the Mireo Plus H prototype bring to rail transport?

Nikolaos Papaiordanidis: Mireo Plus H’s on-board power supply and traction components are fed via the underfloor traction container. Providing more than 1 MW of traction power from such a small installation space is already a challenge, and doing so while also saving energy is particularly challenging. We were able to achieve this through the use of innovative silicon carbide semiconductors that take full advantage of the available space and, thanks to low losses, also make the traction system more efficient, which in turn optimizes overall vehicle efficiency.


And how is practical testing shaping up? Is Mireo Plus H ready to go?

Peter Eckert: No, we’ve just started system testing. Working with partners like Rheinisch-Westfälische Technische Hochschule (RWTH) Aachen, we began by testing interactions between associated components in operation simulations. The installed power of the test bed corresponded to about 900 kilowatts. This enabled us to determine realistic vehicle dynamics parameters and use them to derive different operating strategies for the fuel cell system along the lines of comprehensive train operations management. All the systems were operated to the limits of their performance capabilities and analyzed in Aachen, systematically and over a period of several weeks, both individually and in combination. The safety system was also tested and optimized based on multiple measurements of fuel cell parameters.


Nikolaos Papaiordanidis: This knowledge also enabled us to improve the interaction with the high-voltage traction battery. Control of fuel cell performance is based on the vehicle’s operating phases and battery condition. This in turn enables optimal vehicle efficiency throughout all operating phases.

And is the prototype already benefitting from this?

Peter Eckert: Yes, and this will soon be evident in the practical testing that’s part of the new H2goesRail joint funding project that includes Siemens Mobility, Deutsche Bahn AG, DB Regio, and DB Energie. Siemens Mobility will be integrating the new traction kits into the first Mireo Plus H prototypes. The goal of this project is the development, construction, validation, and certification of a hydrogen EMU, followed by a year of passenger service. The necessary hydrogen infrastructure will also be developed, tested, and optimized as a complete H2 rail system capable of fast refueling.