Airbus is developing a multifunctional fuel cell large enough to replace the auxiliary power unit on an A320, with the potential to reduce total aircraft fuel use by up to 15%.

That’s because the by-products of generating electricity will include clean water for aircraft use, and nitrogen for fuel tank inerting and fire suppression, replacing today’s Halon-based fire extinguishers. The 100kW fuel cell will also generate enough power for the autonomous electrical taxiing system now in development.

Flight tests will begin around 2015 with the fuel cell installed in the cargo hold of an A320. The rest of the installation will include a hydrogen tank, heat exchangers and fans in the tailcone.

Airbus is partnered with Germany’s DLR aerospace research institute and Parker Aerospace for the trials. It is already cooperating in an international network together with other airframers, engine manufacturers, aerospace suppliers and aviation authorities to pave the way for the certification of fuel cells on commercial aircraft.

Airbus last experimented with fuel cells in 2008, when it flight-tested a 25kW cell in DLR’s A320 research aircraft. Michelin was also a partner in those trials, where the cell was mounted on a cargo pallet.

The fuel cell is of the Proton Exchange Membrane (PEM) type, and works very similarly to a battery. It provides a direct conversion hydrogen into electrical energy.

The efficiency of this process is not limited by the thermodynamic constraints of combustion engines and consequently achieves a fuel-to-electricity efficiency two to three times higher than current engine/generator combinations.

The fuel cell does not have to be recharged once empty, as hydrogen and oxygen/air are continuously supplied to the fuel cell stack, allowing continuous operation.

A mockup of the fuel cell is being unveiled here at ILA 2012 on the BMWi (Bundesministerium fuer Wirtschaft und Technologie) booth Hall 4/4303.