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English   Mercedes-Benz Citaro FuelCELL-Hybrid bus
01.08.2009 von admin

New combination of fuel-cell and hybrid bus technology

The new Mercedes-Benz Citaro FuelCELL-Hybrid embodies the genes of not only the proven fuel-cell-drive Citaro, but also the latter's pioneering ancestor, the NEBUS, and the current Citaro G BlueTec Hybrid. It brings them together to form a new whole and sets standards for the development of drive systems for urban buses.

Hydrogen storage capacity reduced despite increased operating range

As in the first-generation fuel-cell-drive Citaro, most of the technical components of the Citaro FuelCELL-Hybrid are accommodated out of the way under stylish panelling on the reinforced roof of the bus. The pressurized hydrogen tanks are situated at the front end. These are the only elements of the fuel-cell system to have been taken over directly from the predecessor model, all the other compo­nents having been newly developed.

As the drive technology of the Citaro FuelCELL-Hybrid cuts fuel consumption considerably, it has been possible to reduce the number of tanks from nine to seven with a total capacity of 35 kg of hydrogen.

Mercedes-Benz Citaro FuelCELL-Hybrid: Tank System

Lithium-ion batteries for energy storage

In a first for fuel-cell buses, the traction batteries situated immediately behind the hydrogen tanks use lithium-ion technology. Their capacity of 27 kWh allows them to supply the electric motors with a constant 120 kW and is sufficient for the Citaro FuelCELL-Hybrid bus to run for several kilometres on battery power alone. In order to maximise performance and efficiency, the batteries are water-cooled as the optimum temperature range for lithium-ion batteries lies between 15 and 55 degrees Celsius.

Two highly efficient fuel-cell stacks

The heart of the drive system of the Mercedes-Benz Citaro FuelCELL-Hybrid is to be found in the form of the two fuel-cell stacks to the rear of the passenger-compartment air-conditioning system which is situated in the centre of the roof. Although adjacent to each other, the stacks function independently. They, too, deliver sufficient power for continuous operation of the electric motors at 120 kW. Each stack contains 396 individual fuel cells. Situated between the stacks are the metering systems for the hydrogen as well as the air feeds to the fuel cells.

The fuel-cell stacks of the Citaro FuelCELL-Hybrid differ significantly from those of the previous bus generation. Their service life has been extended by some 50 per­cent to at least six years. Their efficiency has also been increased consider­ably: it now attains an impressive 51 to 58 percent compared with 38 to 43 per­cent for the first generation.

Heat exchangers to the rear of the stacks use the waste heat from the fuel cells to heat the passenger compartment. If no heating is needed or if the available heat is surplus to requirements, four fans evacuate the hot air. The exhaust at the rear of the bus emits no pollutants whatsoever; the only exhaust emission is harmless water vapour.

Mercedes-Benz Citaro FuelCELL-Hybrid: Fuel Cell and Cooling System

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