When I was learning to drive about 35 years ago,
I read an instruction in the British Highway Code, which struck me as very sensible. It said
"always give way to trains". It's advice that I've followed carefully ever since,
and so far it's stood me in very good stead! An equally insightful piece of commentary,
this time from the aviation industry, comes from this report at the website flight global.
It says this - "power failure in mid-flight is a major risk engineers want to avoid".
That breath-taking piece of wisdom was referring specifically to the problem of
trying to power a long-haul commercial aircraft with lithium-ion batteries instead of jet fuel,
and it's a challenge that's becoming a lot more relevant now that the world has started to pick
its way carefully out of the last 15 months of chaos. As nations try to rebuild their economies
and infrastructure in a greener more sustainable way the question of low or zero carbon aviation
is arguably higher on the agenda of our national governments now than it ever has been. And those
long-haul flights to far away destinations that so many folks are so desperate to jump onto are
just not suitable candidates for the lithium-ion batteries that are used in electric road vehicles.
They're just too heavy for intercontinental flights. So for some time now the aviation
industry has been trying to develop hydrogen as an alternative fuel source to replace the fossil fuel
derived kerosene used in aircraft today, and now the aviation giant Airbus has upped the stakes by
confirming that they're aiming for commercial hydrogen airliners to be in service by 2035.
So is that a realistic ambition? Hello and welcome to Just Have a Think. According to
research carried out in May 2020 by consultancy firm McKinsey and Company on behalf of a European
Commission project called Clean Sky, the engines in modern aircraft emit just over three kilograms
of carbon dioxide for every kilogram of fuel burnt during a flight. They also emit nitrogen oxides,
or NOx, water vapor and soot at high altitudes, all of which contribute to atmospheric warming
either by impacting the ozone layer or by creating dirty contrails that radiate heat.
The latest scientific evaluations suggest that the non-CO2 emissions from kerosene-fuelled aircraft
could have a total effect between two and four times as large as the impact of the CO2 emissions
alone. That means aviation accounts for somewhere between three and seven percent of total global
CO2 equivalent emissions from human activity, which is between two and four billion tons of
CO2 every year. Switching to synthetic fuels made either from biofuels or from hydrocarbons derived
from direct air carbon capture doesn't change the NOx emissions of an aircraft engine, but initial
studies of hydrogen combustion-powered aircraft show that NOx emissions can be reduced by as much
as 80% without large concessions in efficiency. And when a hydrogen fuel cell propulsion system
is used there are no NOx emissions at all. The reverse is true with water vapor though.
Hydrogen combustion and hydrogen fuel cells emit about two and a half times more water vapour
than synthetic fuels or kerosene. Having said that, the McKinsey report points out that
although by dint of sheer volume in the atmosphere water vapor is the predominant greenhouse gas,
individual water molecules themselves are actually 10 times less potent than CO2 molecules. Initial
simulations of hydrogen combustion show that the ice crystals in their contrails are heavier,
which means they fall back to earth more easily. Those contrails don't contain any soot either,
so they're more transparent. The result is a 30% to 50% reduction in impacts from contrail
and cirrus formation compared to kerosene aircraft. And in the case of fuel cells
the vapor can actually be contained and managed within the aircraft itself. Then there's take-off
and landing. The McKinsey research showed that, compared to kerosene, synthetic hydrocarbon fuels
emit a little less particulate matter but don't reduce the other pollutants at all,
whereas hydrogen emits lower or even zero NOx, much lower harmful particulate matter, and far
fewer non-methane volatile organic compounds or NMVOCs as they're known. Now I should give
a little bit of credit to lithium ion batteries at this stage rather than writing them off
completely for powered flight. They don't cause any local pollution or atmospheric warming at all,
and in fact they may well represent a very good solution for short-haul flights of less than
about a thousand miles. But 80% of the aviation industry's pre-COVID emissions came from long-haul
flights, and according to studies carried out by the European Union, if the pre-COVID
global aviation industry was a country it would rank among the top 10 greenhouse gas emitters.
So hydrogen has become the development fuel of choice for most of the major industry players.
Kilogram for kilogram it's got three times the energy density of kerosene,
which sounds great, but it's also got a higher volume compared to kerosene, which means larger
fuel tanks are needed. And that can fundamentally affect the entire design of an aircraft.
Engine makers and aircraft builders, including Rolls-Royce, Boeing and Airbus
are all working on the challenge, but until recently the general consensus was that we
wouldn't see hydrogen planes in commercial service until at least 2050. So this latest 2035 target
from Airbus brings the whole project forward quite a bit. The projection was made by Glenn Lewellen,
Airbus Vice President of Zero Emissions Aircraft... "we see it as something that
the airlines are asking for from us and on top we see it as a moral obligation that we need to bring
climate neutral flying to society". He believes hydrogen is the best pathway for decarbonization
but he also made the very important point that success would depend heavily on the widespread
adoption of hydrogen fuel in many other industries in modern economies combined with the continuing
decline in the cost of wind and solar power to drive the electrolysis needed to produce green
carbon-free hydrogen rather than grey carbon-heavy hydrogen derived from steam-reforming methane.
Nevertheless, Llewellyn does expect the cost of hydrogen to drop significantly in the coming years
as production increases around the world. His team has developed three different aircraft models,
each designed to cater for a specific sector of the aviation industry. All three concepts
are hybrid hydrogen aircraft powered by hydrogen combustion through modified gas turbine engines.
Liquid hydrogen is used as the combustion fuel while hydrogen fuel cells create electrical power
that complements the gas turbine resulting in a highly efficient hybrid electric
propulsion system. For flights up to about a thousand miles carrying 100 or so passengers
a propeller system known as a turbo prop has been shown to be the most efficient,
least polluting, and most climate friendly option. Two hybrid engines drive eight bladed propellers
to provide the thrust, with the liquid hydrogen storage and distribution system housed behind
the pressurized cabin bulkhead. For long-haul intercontinental flights of more than 2000 miles
Airbus are developing a couple of options. The first is a fairly traditional looking turbo fan
design carrying about 200 passengers. It'll have an elongated fuselage to hold the higher volume
of hydrogen fuel with their hybrid hydrogen system powering a jet engine on each wing.
The second option is this futuristic design, known as a 'blended wing' body,
where the wings merge with the main body of the aircraft allowing fuel to be stored
across the entire underside of the fuselage. It'll also have a range of about 2 000 miles
and there'll be a very wide open cabin space with enough seating capacity for about 200 passengers.
Airbus plans to invest hundreds of millions of Euros in hydrogen up to 2025 to determine which
aircraft to bring to the market first. After that, according to Llewelyn, the investment
will scale up to multiple billions through to 2035. "Honestly though, we can't do this
on our own. We need regulators, airports, energy suppliers, technology partners, and it's through
working with all of these colleagues that really this is going to become reality. Llewellyn argues
that airports shouldn't wait though. He reckons they should start using hydrogen to decarbonize
their ground transportation ecosystem immediately. He says that will enable airports to scale up
their hydrogen infrastructure in preparation for the hydrogen aircraft that will be arriving
by mid-2030s and he suggests that if they're smart about how they install that infrastructure
then they could become very profitable hydrogen hubs servicing adjoining cities.
No doubt some of you will be shouting the word 'safety' at the screen right now. And quite right
too! Although hydrogen is non-toxic and no more or less dangerous than jet fuel or methane gas,
safety will still, unsurprisingly, be the overwhelmingly most important consideration in
the development of hydrogen-powered aircraft. No commercial aircraft has any chance of getting off
the ground until it's been through the rigorous testing required by aviation industry regulations.
If all those hurdles can be overcome though, then hydrogen-powered aircraft could make up
a very significant proportion of the global fleet in the coming decades. And if older existing jet
engines are converted to synthetic fuels instead of kerosene for the remainder of their serviceable
lifetime, then according to the McKinsey study, even with the expected uplift in passenger flights
over the coming decades, aviation's climate impact would drop to the equivalent of about 2.7 gigatons
per year of CO2 equivalent versus 5.7 gigatons in their baseline scenario without hydrogen and
just with efficiency improvements to existing fossil fuel powered engines. And if the entire
aviation industry steps up to match the ambition and urgency shown by Glenn Llewellyn and his
team at Airbus, instead of kicking the can further down the road like Boeing seemed to be doing, then
those CO2 emissions could be almost completely eliminated by mid-century. Now I know there's a
lot of folks out there who have a forensic level of detailed knowledge about the aviation industry,
and I'm sure you're chomping at the bit to point out any variables or challenges that I may have
missed here. If that's you, or if you work in the aviation industry and you have views to share,
then jump down to the comments section below and leave your thoughts there. That's it for this
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