Alpine Challenge: Mercedes-Benz eCitaro fuel cell defies extreme cold and steep passes

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• On the road with the e-bus test team
• Good energy balance thanks to thermal management and high recuperation
• Destination Bolzano is a hydrogen hotspot
• Consistently positive test result

Leinfelden-Echterdingen – At the beginning of June, Mercedes-Benz showcased the new #eCitaro fuel cell for the very first time, the first regular-service bus with a fuel cell to extend the range. Before the start of series production, the #eCitaro fuel cell had to pass numerous functional and safety tests. This also included a winter alpine crossing – a test run with many challenges.

The cold alpine air envelops the yellow, low-floor articulated bus, making it seem like a foreign object in the extensive car park on the Plan de Gralba at an altitude of 1795 metres above sea level in the South Tyrolean Alps. While driver Andreas Hoffmann is eagerly scraping ice off the windows, a small white cloud of steam curls upwards from the roof structures of the bus – an unmistakable sign that the fuel cell on the roof of the bus has begun its work and is now generating electricity from hydrogen and oxygen in the air – emitting only steam. This articulated bus is a test vehicle, one of four prototypes of the Mercedes-Benz #eCitaro fuel cell.

The first electric bus in which a fuel cell system extends the range has just undergone one of a range of tests and passed with flying colours: after a night at temperatures far below freezing, the electric drive system and fuel cell started up smoothly.

At the beginning of 2023, a team of Mercedes-Benz test engineers went to the Alps with the #eCitaro fuel cell in order to test its cold-starting behaviour in winter temperatures and to try out the newly developed thermal management system. At the same time, the runs at elevations of more than 1700 metres above sea level were intended to provide insights into the function of the fuel cell system at extreme altitudes. The new drive system also had to prove its performance on demanding mountain pass runs with uphill and downhill gradients of as much as 15 percent. Last but not least, the energy consumption was of great interest in these challenging conditions.

On the road with the e-bus test team

“During the journey, test engineers constantly monitored countless measuring points and data,” explained test manager Jonas Steinki. Besides the temperatures of the battery, fuel cell, engines and passenger compartment, these also include the energy consumption of the drive, the heating and other auxiliary consumers, the charge level of the batteries and the fill level of the hydrogen tanks. Test engineers Rainer Bickel, Stephan Lutz and Hannes Mayer continuously checked the most important parameters of the fuel cell system, drive, thermal management and heating on their monitors, looking for anomalies and comparing the data with the calculated target values.

The test run that lasted several days, started with crossing the Alps from Neu-Ulm via Füssen, the Fern pass and the Reschen pass to Bolzano. The combination of battery and hydrogen was designed to be able to cover the 360-kilometre route. Nevertheless, was is difficult to estimate how the energy consumption would develop on the long and steep passes at temperatures below freezing. To err on the side of caution, the team decided to partially recharge the high-voltage batteries at the Allgäuer Tor service station.

Good energy balance thanks to thermal management and high recuperation

On the way across the Fern pass, it soon became clear that the #eCitaro fuel cell was capable of dealing with the demanding route even better than expected. “Despite the gradient, the fuel cell operated within the most efficient power range of 20 to 30 kW,” explained Rainer Bickel, pointing to the corresponding value on the monitor. "What's more, the new thermal management reuses the waste heat from the fuel cell to control the interior temperature. The electric heating is therefore hardly used so that the overall energy consumption of all the auxiliary units, such as heating, steering and compressor, remains at a very low level."

The #eCitaro fuel cell also demonstrates its strengths on downhill gradients. During braking, recuperation increases to as much as 285 kW. This means: the motors, of which there are four in all, on the two drive axles now act as alternators and charge the batteries with up to 285 kW – almost twice as much as a fast charging station. “That’s more than enough,” Rainer Bickel reported. “So as not to put too much strain on the batteries, we have limited the recuperation output to 285 kW.”

The positive energy balance lasted to the target of crossing the Alps at Bolzano: after 368 kilometres and opportunity charging with around 55 kWh, the battery charge indicator still showed 56 percent SoC (state of charge). The hydrogen tanks were also still amply filled at 42 percent.

Destination Bolzano is a hydrogen hotspot

Bolzano turned out to be the ideal destination for the winter test run. With a public hydrogen filling station directly next to the Bolzano South motorway junction and another H2 filling station at the depot of the Bolzano-based Sasa transport company, it has one of the best H2 infrastructures in Europe. Added to this, the hydrogen available here comes exclusively from renewable sources – primarily electrolysis using hydroelectric power. Moreover, the surrounding Dolomites with their steep mountain passes and high elevations offer ideal conditions for altitude testing of the fuel cell system and further tests across challenging topography and at low temperatures.

“Yet the winter trial is just one of several tests that the #eCitaro fuel cell has to undergo before it enters series production starting in the summer,” stressed Shahrukh Javed, Project Manager for the #eCitaro fuel cell. “In particular, the hydrogen tanks and the fuel cell system have successfully completed extensive safety tests, some of which go beyond those required by law.” These include impact and vibration tests as well as a sled test with the fastening system, which simulate an accident. For testing under hot conditions, the #eCitaro fuel cell went to the #truck climate chamber of our #truck colleagues at Wörth in Rhineland-Palatinate.

Consistently positive test result

Even so, Javed is convinced that notwithstanding the climate chamber with its roller dynamometer, there is still a need to test under real conditions: “the many different measurement results and findings that we can gain from the high altitudes, steep routes and low temperatures on this trip are invaluable.” The project manager takes a positive view of crossing the Alps and the various test runs on alpine passes: "the #eCitaro fuel cell met the challenges of this alpine run with flying colours. Thanks to the new energy management system, the fuel cell mainly operated in the most efficient range between 20 and 30 kW, even on long and steep inclines. The new thermal management system was shown to be an important building block for energy efficiency by using the waste heat from the fuel cell optimally to control the temperature in the passenger compartment. On this demanding test journey, the #eCitaro fuel cell exceeded our expectations in terms of range as well as the efficiency of the drive and the fuel cell system."