Zero emission aeroplanes that use ammonia as jet fuel rather than kerosene could take to the skies 'within years', British scientists claim.
OGN Daily recently reported on the first electric plane flight and a larger hybrid hydrogen powered aircraft; it now seems a third plausible solution for dramatically reducing the carbon footprint of air travel is within grasping distance.
A collaboration between Oxford-based Reaction Engines and the UK Science and Technology Facilities Council could see ammonia replace kerosene as jet fuel. Unlike kerosene-based jet fuel, ammonia is less of a fire hazard and, in even better news, burns without releasing the greenhouse gas carbon dioxide that contributes to climate change. The third piece in the good news jigsaw is that a switch to ammonia would only require minor additions to conventional jet engines, meaning airlines could make use of the cleaner fuel without needing to completely replace their current plane fleets.
In order to be burned in an engine, ammonia needs to be mixed with hydrogen - which can be released from the ammonia itself using heat and a catalyst. The researchers are proposing, therefore, to use a heat exchanger to warm up the fuel en route to the engine, followed by a so-called 'cracking reactor' to split some of the ammonia into hydrogen and nitrogen. The fuel mix can then be ignited to drive the engine, with the only waste products being nitrogen, water vapour and perhaps some nitrogen oxides - although the latter can be removed from the exhaust using more ammonia.
"The fuel could actually scrub its own emissions," said Reaction Engines' Dr James Barth.
Ammonia does have a lower energy density than conventional jet fuel - meaning that aircraft powered by the novel fuel would have a slightly shorter range. However, Dr Barth explained, ammonia fares well in comparison with other green aircraft solutions - including the more expensive fuel hydrogen and battery-power - and ammonia-powered planes would be perfectly suitable for short haul flights.