Easy Tech: The Fuel Cell Technology of the GLC F-CELL

„Ahmet, your car smokes like a shisha bar!” Right, but the GLC F-CELL (GLC F-CELL: Wasserstoffverbrauch kombiniert: 0,34 kg/100 km; CO2-Emissionen kombiniert: 0 g/km; Stromverbrauch kombiniert: 13,7 kWh/100 km.*) doesn’t “smoke”. The emissions are H2O: Water vapor.

Especially when it’s cold, the warm water vapor condenses in the cold ambient air. For an amateur, it seems like fog. As project engineer at Mercedes-Benz Fuel Cell GmbH, the cause of this “fog” is my specialty: The fuel cell system of the GLC F-CELL.

For the GLC F-CELL we developed a completely new fuel cell system. What’s special about it?

The GLC F-CELL is the first vehicle worldwide that contains a plug-in hybrid battery. Thereby, two different energy sources are available to drive the electric engine. That’s why we’re not dependent on hydrogen filling stations, but rather we can refuel at any charging station or socket available.

How does the fuel cell system of the GLC F-CELL works?

Everybody knows the electrolysis from chemistry class: Water can be split into hydrogen and oxygen when interfered with electricity. We use these two gases to gain electricity in the reverse process. Thus the fuel cell does nothing else than conducting the reaction between hydrogen and oxygen.

The oxygen needed for the reaction, is pulled in from the outside and is provided by an electric turbocharger. The hydrogen necessary for the fuel cell is provided by the hydrogen tanks.

The fuel cell is a PEM fuel cell with Proton Exchange Membrane, meaning that its membrane is only permeable for protons. The hydrogen is split into protons and electrons. Protons migrate from the anode side via the membrane to the cathode side in order to get to the oxygen. The electrons take their way around the membrane, resulting in an electricity flow. This electricity is either used for the electric drive or to charge the battery.

The essential components in the GLC F-CELL are the fuel cell, the hydrogen tanks and the battery. How do they interact in operation?

The Fuel Cell
The fuel cell system mentioned above refers to one PEM fuel cell. In order to maximize the electricity flow, there is a fuel cell stack in the vehicle. This stack contains many single fuel cells. The actual reaction between hydrogen and oxygen takes place in those fuel cell stacks, in which the chemical reaction energy is converted (also known as cold or catalytic combustion). Therefore, in contrast to the battery, the fuel cell is no energy storage but rather an energy converter.

The Hydrogen Tanks
The hydrogen is located in two tanks: one long container and one cross container. The cross container is installed under the rear seat bench, the long container underneath the center tunnel. Both tanks are able to absorb 4.4 kg hydrogen, which can be fully refueled within three minutes at 700 bar.

The Battery
The lithium-ion battery of the GLC F-CELL is located under the car’s trunk. It has a capacity of approximately 13.5 kWh and can be charged while operating: either through the fuel cell or the recuperation, namely the brake energy recovery. The major task of the battery is the buffering of the electric energy and the additional driving power.

The driver has the opportunity to choose between four different operating modes. What does each mode stand for?

In HYBRID operating mode, the power of the vehicle is provided by both energy sources, namely the fuel cell and the battery. BATTERY means that the vehicle is powered purely battery-electric while the fuel cell is switched off. In F- CELL mode, one drives almost exclusively with hydrogen, whereby the energy of the fuel cell holds the charge level of the battery constant. And in CHARGE mode, the battery is charged via the fuel cell. The recuperation should be mentioned as well. It’s available in every operating mode and makes it possible to regain the energy when braking or coasting, and storing it in the battery.

Which mode is used when – and who decides: System or Driver?

Basically, the driver can decide at any time which operating mode he or she wants to use. But the vehicle is able to make this decision itself: Depending on the gas pedal requirement of the driver, the intelligent system of the GLC F-CELL is able to determine how much energy is currently needed. And from which source this energy has to be provided – without the driver’s notice.

The GLC F-CELL doesn’t know whether you’re driving on a motorway, highway or in a 30 km/h zone. Only the gas pedal requirement of the driver is significant for the vehicle: that’s how the required power is calculated. On this basis, the GLC F-CELL decides whether e.g. 70 percent of the power should be provided by the fuel cell and 30 percent by the battery. Or whether it’s driving exclusively battery-electric in BATTERY mode.

Electric Mobility: Battery vs. Fuel Cell?

I don’t perceive the battery and the fuel cell as competitors: They complement each other perfectly – the GLC F-CELL is the best example! For short-distance drives the battery is much more appropriate as the fuel cell. During long-distance drives, the fuel cell technology shows its strengths: a high range and a fast refueling time.

With the GLC F-CELL, we introduced a vehicle that is suitable for everyday use. When I took the GLC F¬-CELL at home for the first time, in order to simulate customer road behavior over several weeks, I didn’t wanted to give it back. Commuting, shopping and travelling: not a problem!

*Figures for fuel consumption, electrical consumption and CO2 emissions are provisional and were determined by the technical service for the certification process in accordance with the WLTP test method and correlated into NEDC figures. The EC type approval and a certificate of conformity with official figures are not yet available. Differences between the stated figures and the official figures are possible.

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Ahmet Demirezen is project engineer in the development of the fuel cell system at the Mercedes-Benz Fuel Cell GmbH. Concerning the fuel cell technology, he is fascinated about the complex procedure, which is controlled by the vehicle in a very intelligent and efficient way. A real experience for the driver!