Mercedes-Benz reports on 3.3M km of B-Class Fuel Cell testing, looks ahead to next generation

While Hyundai, Toyota and Honda seized much attention over their presentations of fuel cell rollout plans (in the case of Hyundai) and concepts (in the case of Honda and Toyota) at the Los Angeles and Tokyo auto shows, Daimler used EVS27 in Barcelona as a forum to report on its 3.3 million kilometers (2 million miles) of experience with the Mercedes-Benz B-Class Fuel Cell fleet as well as the main technical targets envisioned for the next generation fuel cell electric car.

Mercedes-Benz began production of the B-Class F-Cell in 2009; 200 units of the vehicle were produced under standard production process at Mercedes-Benz facilities and delivered to customers worldwide.

The B-Class-based vehicle had light modification to support the integration of the fuel cell system, the hydrogen tank system as well as the electric drive. The B-Class F-Cell vehicle represented Mercedes-Benzs second-generation fleet experience. The earlier A-Class accumulated more than 2 million kilometers (1.2 million miles) in fleet testing.

In total (fleet testing plus developmental testing), the Daimler hydrogen fuel cell fleet has accumulated more than 9.0 million km (5.6 million miles).

Based on an optimized, more compact fuel cell system presented by Mercedes-Benz in its F 600 HYGENIUS research vehicle in 2005, the 80 kW stack module in the B-Class F-CELL is around 40% smaller, but develops 30% more power output and cuts fuel consumption by 16% compared to the A-Class stack. Stack lifetime has increased to more than 2,000 hours.

Comparison of the performance improvement between the A-Class F-Cell and B-Class F-Cell. Source: Daimler AG. Click to enlarge.

The electric motor has a continuous / peak performance of 70 kW / 100 kW (94 hp / 136 hp) and a maximum torque of 290 Nm (214 lb-ft). Range (NEDC) is 385 km (239 miles) and refueling time is about three minutes. The fuel-cell car uses a lithium-ion battery pack with an output of 35 kW and a capacity of 1.4 kWh to boost power and recover braking energy.

The B-Class fuel cell stack comprises 440 cells connected in series, with carbon-based bipolar plates. The air system is an electric air compressor including silencers, power electronic, piping and noise cover. The compressor technology is a constant displacement screw which through a clutch is connected to the electric motor.

One of the main tasks of the operating strategies of the stack is to maintain a defined humidity level to avoid the drying out of the fuel cell membrane or the flooding of electrodes. Both cases would lead to performance loss and cause additional risk for permanent degradation. Mercedes-Benz engineers developed the control strategy in such a way that there is always a well-defined balance between coolant temperature, air and hydrogen flow rates and pressure of cathode and anode at each individual load point.

Fleet results. The greatest number of the vehicles are in operation in California around Los Angeles. All failures are tracked and statistically evaluated. Reliability of the fuel cell system has grown steadily during fleet operation, Mercedes-Benz says. To further improve the reliability of the fuel cell system, new components will be required.

Average fuel consumption of F-Cell World Drive vehicles on different continents. Source: Daimler AG Click to enlarge.

Fuel consumption of each vehicle was tracked and clustered for each continent; the results show that the lowest fuel consumption was achieved during the operation in the USA. The good fuel economy is caused by the long distant cross country highway operation at constant speed and a low number of stops in combination with the speed limit. In some cases, fuel consumption was less than 1 kg/100 km.

In Europe the fuel consumption was a slightly higher than the other continents, due mainly to higher traffic density with less constant speeds and shorter cross country distances between cities and towns.

Observations on hydrogen infrastructure from the fleet demonstration included:

• The infrastructure used with the demonstrations is not sufficient for the envisaged commercialization roadmap.
• For full customer acceptance convenient H₂-filling stations distributed across a wide area are needed.
• Repair times in case of a station breakdown need to be shortened.
• The purity of H₂needs to be discussed in a more detailed and bilateral (station-side/vehicle-side) way.
• The compressor is the component that fails most often.

Path forward. The next generation of fuel cell technology, targeted for application in vehicles for the market introduction, is under development in the framework of the co-operation between Daimler, Nissan and Ford Motor Company, announced in January 2013.

The next generation system will incorporate technology changes as well as an improvement in packaging which will allow the next-generation fuel cell system to be integrated in the front of the car.

The next-generation fuel cell system will show a significant reduction is size and subsequent improvement in packaging. Source: Daimler AG. Click to enlarge.

Resources

• M. Venturi, C. Mohrdieck, J. Friedrich (2013) Mercedes-Benz B-Class Fuel Cell: the world largest hydrogen vehicle fuel cell fleet experience (EVS27 Symposium)