Environmentally friendly aircraft: hydrogen fuel cells for airplanes

Hy-BirdLONDON, UK (RUSHPRNEWS) 09/22/2008–Fuel cells can already be used to power motor vehicles, but what about a commercial airliner? Fuel cell powered airplanes may be nearer than you think. The first manned flight powered by a hydrogen fuel cell was flown in March 2008. A recent study explains how this energy source can be used in small aircrafts, potentially reducing greenhouse gas emissions in aviation.

Hydrogen fuel cells are environmentally friendly, alternative power source systems which produce no emissions other than water. In this project, researchers from Boeing tested a fuel cell-based propulsion system, especially designed for aviation, by converting a conventional motor glider into a fuel cell demonstration airplane. Two power sources, a PEM (Proton Exchange Membrane) fuel cell and a Li-ion (Lithium-ion) battery, supply energy to an electric motor, which drives the aircraft propeller. Primary power is produced by the fuel cell system with extra power supplied by the batteries during take-off and the climb to level flight.

The fuel cell system converts chemical energy from the reaction between hydrogen and oxygen into electrical energy. Hydrogen gas is stored under high pressure to minimise the weight of the system. The oxygen is drawn from the surrounding air.

Li-ion batteries are the secondary power source. These are rechargeable batteries, which have to be charged on the ground before each demonstration flight. They are used as auxiliary power sources, supplying around half the power during take-off and climb but are then disconnected once cruise altitude is reached. Power in level flight is then solely supplied by the fuel cell system.

Before the first demonstration flight, researchers thoroughly tested the fuel cell under steady state and dynamic operating conditions to prove that such a system could reliably supply the power demanded in all operating conditions during flight. The optimum on-board location of the fuel cell system components was determined during tilt bench tests.

Subsequent bench tests of the whole system showed that the electrical system, fuel cell system, auxiliary batteries, control system and instrumentation system all operated correctly in all the simulated flight stages. In addition, these tests demonstrated that if there was a failure of the fuel cell during takeoff, the Li-ion battery had sufficient power for take-off and climb to 300m, an altitude high enough for the pilot to perform a 180º turn and make an emergency landing on the runway.

This study gives details of the challenges overcome by the researchers in designing a hybrid fuel source capable of meeting strict weight and size limitations found in an aircraft environment, having a correct thermal management and electrically integrating the two power sources, when working together, that is during take-off and climb.

Source: European Commission, Environment DG

PHOTO: Hy-Bird