Rail Transport – Alternatives to Diesel
Author: Joachim Geiger
Electric traction under an overhead contact line is the ultimate benchmark in European rail transport. If only there weren’t the many main and branch lines that still use diesel engines. More and more rail operators are now revamping their fleets – alternative drives for locally emission-free train travel are in demand.
Green conscience is a powerful motivator for the rail industry, too. Are you transporting people and goods quickly, safely, and climate-neutrally on tracks? Then electric traction is the preferred choice. According to UNIFE, the European Rail Supply Industry’s umbrella organization based in Brussels, on average half of the lines in Europe are electrified with overhead lines. Countries such as Switzerland, Belgium, and the Netherlands have a comparatively short network of lines, but offer a very high degree of electrification. In Germany and France – the European front runners with train lines of around 39,000 and 27,000 kilometers respectively – the proportion of sections with overhead lines is a moderate 61 and 59 percent. The bottom line is that 80 percent of all rail traffic in Europe draws its traction energy from external power supplies. At first glance, that sounds very sustainable. But a closer look reveals that the real ecological challenge is hidden in the remaining 20 percent. After all, trains have to roll across the country on main and branch lines even where there’s no contact wire. That’s mainly a job for diesel traction. In fact, there are 25 diesel-powered series with around 4,400 railcars on the road in Europe – around half of which operate in Germany
A massive upheaval lies ahead of non-electrified rail transport
Most European rail companies would prefer to phase out their diesel locomotives sooner rather than later. Deutsche Bahn (DB), for example, has set itself the goal of phasing diesel out by 2040. There are several options for realizing this ambition. For example, sections of track and terminal stations could be electrified by extending overhead lines. However, with costs of up to two million euros per kilometer, this would be an expensive undertaking. DB is therefore currently planning to electrify only around 760 additional kilometers of track by 2030. Instead of investing a lot of money in infrastructure, rail operators prefer to focus on a new generation of vehicles. Locomotives that can handle multiple driving modes – like electric traction under the overhead line and driving with alternative propulsion on sections of track that do not have their own contact wire – are very popular. In a market study presented in August 2020, the Hamburg-based consultancy SCI Verkehr predicts a massive transformation in non-electrified rail transport. According to the study, trains with battery technology (Battery Electric Multiple Unit/BEMU) and hydrogen fuel cell systems (Hydrogen Electric Multiple Unit/HEMU) are expected to catch up with diesel multiple units in the new vehicle business in Western European core markets by the middle of the decade.
Rail experts see the versatile battery trains at a slight advantage
Which alternative drive will ultimately come out on top in this race? Relevant studies see the technological concept of battery electric trains as having the advantage. A BEMU is basically an electric railcar with a rechargeable battery as energy storage. On electrified lines, the vehicle draws its traction current from the overhead contact line. When it reaches a section without its own overhead contact wire, the train automatically switches to battery mode – in this case, the storage batteries supply the energy for further propulsion. Charging takes place under the overhead line while the train is moving or stationary, with charging powers of one megawatt and more. Another charging option is offered by so-called electrification islands, for which individual sections of a line would have to be specially equipped with contact wire. Special charging stations are also a possibility – the first examples are already being tested in southern Germany. Range remains the crucial issue for the use of battery trains: Most manufacturers calculate a range of 80 to 120 kilometers that a vehicle can travel in one go. Since around 90 percent of non-electrified routes in Germany are shorter than 70 kilometers, it should be possible to bridge most power gaps in the rail network with a BEMU. A perfect reference in terms of range is the Flirt Akku battery train from vehicle manufacturer Stadler, which made it into the Guinness Book of Records late last year with a record-breaking run. A range of 224 kilometers was measured, which the vehicle covered in battery mode on the route from Berlin-Gesundbrunnen to Warnemünde in sub-zero temperatures and snowfall.
In terms of range, the hydrogen train clearly demonstrates its strengths
Even if battery-powered trains demonstrate enormous performance capability, they can’t always replace a compression-ignition engine. After all, every diesel route has its own special driving requirements. Topography, routing, and climatic conditions, as well as the charging infrastructure obviously have an impact on range. “In the case of higher energy requirements, such as those needed for strong grades or extreme climatic conditions, a battery-powered train can sometimes run out of breath,” knows Dr. Christoph Flink, Vice President Hydrogen Economy Program Management in DEKRA’s Service Division Industrial Inspection. As the expert explains, a hydrogen train would have no problems with such a scenario – after all, the range can be up to 1,000 kilometers.
DEKRA Rail in Utrecht, Netherlands, has also added hydrogen trains to their agenda. At the beginning of 2020, experts from the railway division accompanied a pilot project of the Groningen province, which investigated the suitability of a train powered by green hydrogen on the train line from Groningen to Leeuwarden. “We officially accompanied the project as experts in matters of technology, safety, and approval,” reports Jean-Paul van Hengstum, Managing Director of DEKRA Rail. The clear result: Hydrogen trains are a sustainable alternative to diesel operation.
In technical terms, the HEMU ranks in the category of electric motor drives – fuel cell and battery work hand in hand during operation. When there is a power peak during acceleration, the electricity from the fuel cells alone is not sufficient. The battery must provide additional capacity. Only when less traction is required, does the fuel cell recharge the battery. However, drawing power from the overhead line is out of the question for a HEMU – the vehicle concept simply does not provide for a current collector. The hydrogen trains are therefore primarily used on routes without overhead lines, which makes the operating concept exactly the same as for diesel. But why not go one step further with hybridization? DEKRA expert Dr. Flink can imagine that combining hydrogen propulsion with an overhead line could once again significantly increase the efficiency and flexibility of the vehicles.
The diesel engine finds its niche in alternative vehicle concepts
Ultimately, rail operators must carefully examine which climate-neutral locomotives offer the best alternatives on their diesel networks. The Oberelbe Transport Association, for example, has developed a decision paper presented in September 2021 for precisely this purpose together with the Technical Universities of Dresden and Berlin. The paper states that overhead line/battery hybrid vehicles or classic electric trains are preferable to other alternative forms of propulsion from an economic perspective. According to the study, battery-powered trains score points over hydrogen trains primarily because of lower energy and maintenance costs. Incidentally, the range of alternative drive systems is by no means limited to purely electric traction. Rail operators should also keep diesel on their radar. We are talking about locomotives that run electrically on routes with overhead lines, but with diesel engines on other sections. This way, the last mile to the rail customer can be covered by combustion engine, for example. It should also be possible to cover heavier transfer runs. Deutsche Bahn has already ordered 150 Vectron Dual Mode vehicles with these hybrid features from vehicle manufacturer Siemens Mobility.
In Germany, rail alternatives are on the rise
Vehicle manufacturers Alstom, Siemens Mobility, and Stadler all have traction units in their portfolios that can be operated on non-electrified sections with zero local emissions. The order books are filled with orders for BEMU and HEMU. Siemens Mobility will supply 20 Mireo Plus B battery trains to Southwest Germany’s Local Transport Corporation starting in mid-2023. In turn, the Schleswig-Holstein Public Transport Association expects to receive 55 units of the Flirt Akku series from Swiss manufacturer Stadler this year, while the Central Saxony Public Transport Association has ordered eleven Alstom Coradia Continental vehicles. Interest in hydrogen trains is also high. This year, the Local Transport Authority of Lower Saxony plans to replace 14 diesel multiple units on the Weser-Elbe network with the same number of units of the Alstom Coradia iLint hydrogen train. By the end of 2022, the Rhine-Main Transport Association will put 27 hydrogen trains of the same type into regular operation – the Hessians will then be operating the largest hydrogen train fleet in the world. Together with Deutsche Bahn, Siemens Mobility will start the first trial operation with the Mireo Plus H series in Bavaria starting in mid-2023 and in Baden-Württemberg in 2024.
The first purely battery-electric locomotive runs in North America
The credit for putting the first purely battery-electric locomotive on the tracks goes to Pittsburgh in the North American state of Pennsylvania. Vehicle manufacturer Wabtec has developed a battery-powered locomotive that no longer requires any connection to an overhead line. The Wabtec FLXdrive has a battery capacity of a staggering 2.4 megawatt hours and will initially be used primarily in shunting service. But the locomotive could also provide helpful services on the track, as demonstrated by a three-month pilot project in California. In tandem with two diesel locomotives, it traveled more than 21,000 kilometers in a train over hilly terrain with many inclines. The result of the multiple traction was that the use of the electric locomotive reduced diesel consumption by an average of eleven percent, which was pleasing for rail operators. Now Wabtec is planning an electric locomotive with a capacity of more than six megawatt hours.