Saving energy with hydrogen Fuel cells to replace auxiliary power units for supplying electricity in aircraft Fuel cell generator as a replacement for the auxiliary power unit (APU) in the tail of a passenger aircraft.
Alternative methods of electricity generation occupy a central role in the planning for the All Electric Aircraft, with the fuel cell the favourite to win through. Thanks to its unrivalled level of efficiency, it converts chemical fuel into electricity better than any other system. A power supply system based on fuel cells, which would not only replace the auxiliary power units commonly used today but would also continuously generate electricity whether the aircraft is on the ground or in the air, could mean airlines making annual savings counted in millions. Not only that, such a system would feasibly reduce both noise and pollutant emissions from aircraft. A great deal of research and development work is still needed before a fuel cell unit can be built which would have the same output as today’s APUs but would also be as small as shown in this illustration. © EADS In its Celina project, part of the Sixth Framework Programme, the European Union is promoting research and development for chemical batteries of this type for aeronautical applications. Fuel cell systems that derive their energy from pure hydrogen are particularly suitable for mobile use.
If pure hydrogen is not available as such, it is usually separated from primary energy sources such as methanol or other hydrocarbons using reformers. The EADS Research Centre in Ottobrunn near Munich, on the other hand, is investigating the conversion of fuels by means of partial dehydration, which makes for a system that is less complex and bulky – and lighter. In partial dehydration, hydrogen is separated from the jet fuel kerosene. To do this, the process requires catalysts, and here, the scientists want to use commercially available substances such as palladium or platinum. The gaseous hydrogen is fed into the fuel cell, while the liquid hydrocarbon residues are either burned in the engine or returned to the kerosene tank.