The main reason for these projects is not to develop primary power sources for jet-turbine powered aircraft, but to build small, highly efficient fuel cells that could be used to make greener airliners.

ECONOMIST: Electric planes

After one has made every last power plant, jet engine, assembly line and car as efficient as they can possibly be given today's technology, one either hopes for an energy-boosting technological miracle or else starts restructuring the economy.

WSJ: Joseph Sternberg: All the Hot Air in China

It would also need to be only half the size of a conventional jet of similar power, says Dr Lior.

ECONOMIST: A new way to build a greener jet engine