April 3, 2007. Copyright 2007, Graphic News. All rights reserved

Fuel cells offer hope for greener flying
By Mark Rutter
 
LONDON, April 3, Graphic News: With the aviation industry coming under increasing scrutiny from governments and environmentalists for its greenhouse gas emissions, aircraft makers are cranking up their search for greener planes. One technology holding out promise is the replacement of oil-based fuels with a fuel cell. Aerospace company Boeing has just announced that it is preparing to carry out test flights on an aircraft propelled solely by a fuel cell.

Fuel cells generate electricity from an electrochemical reaction in which oxygen from the air and a fuel, usually hydrogen, combine to form water. There are several different kinds of fuel cell, some of which are suitable for particular applications. These range from power stations to power sources for motor vehicles and electronic gadgets. However, all are based on a similar design, consisting of a stack of individual electrochemical cells. By directly converting hydrogen into electricity and heat without combustion, fuel cells are emission-free and quieter than hydrocarbon fuel-powered engines.

Hydrogen can be easily extracted from hydrocarbon fuels such as natural gas or petroleum. This can be done on board a vehicle in a processor attached to the fuel cell, or alternatively in a refinery or chemical plant, and then delivered to and stored aboard the vehicle. The best solution for the environment, though, would be to generate hydrogen from renewable sources, such as solar or wind power, to provide a zero carbon energy source.

Boeing and a number of its European collaborators from several countries have just completed the first phase of the Fuel Cell Demonstrator Airplane research project, which began in 2003. This resulted in the development of a Proton Exchange Membrane (PEM) fuel cell, linked to a lightweight lithium battery, capable of powering a conventional propeller. PEM fuel cells operate at relatively low temperatures so can reach their optimum operating temperature quickly. Added to this, they are compact, able to respond rapidly to varying power demand, and are twice as efficient as internal combustion engines, making them the best option for cars, buildings and small planes at present.

The first flight tests of Boeing's project, scheduled to take place in Spain, will attempt to show that a fuel cell can provide sufficient power for a small piloted motor glider with a wingspan of 16.3 metres (53.5 feet), to cruise at 100 kilometres per hour (62 miles per hour). However, the plane will draw from the lithium battery during takeoff and ascent when additional power is required.

Eventually the research could lead to the production of fuel cells suitable for powering commercial passenger aircraft, although Boeing admits this is some way off at the moment. It is exploring other types of fuel cell that might be suitable for larger aircraft, like the Solid Oxide Fuel Cell (SOFC). These cells work at much higher temperatures than PEMs -- at 800 to 1,000¡C -- and are capable of providing greater power, so are useful for industrial applications. But it is still likely to be a decade or two before the technology is routinely installed in commercial planes.
/ENDS