SAE Update - February 2024 - 30

TECH FOCUS:
AErOSPACE
Can SAFs decarbonize civil aviation?
conservation, and afforestation for
land use. The good news here is
that most biomass is currently
used for traditional domestic
heating and cooking, applications
which can be readily electrified.
Using biomass to replace the vast
quantities of fossil fuel for
electricity generation and road
transport would be impossible.
However, if biomass is reserved for
uses where there is little
alternative to liquid fuels,
principally aviation and shipping,
then these needs could be met
from current production. Biofuels
must transition to second
generation cellulosic feedstocks
while improving land and soil
management.
E-fuels are produced from air
and water, using renewable
electricity to electrolyze water to
produce " green " hydrogen and
capture CO2. Thermo-chemical
processes are then used to
synthesize hydrocarbon fuels
such as kerosine. The vast
majority of the cost and energy
in this process is consumed by
the electrolysis of hydrogen,
some of which ends up in the
final hydrocarbon fuel, and some
of which is consumed by the
thermos-chemical synthesis
processes. At the energy system
30
February 2024
or economy level, it therefore makes sense to think of
e-fuels as a form of hydrogen storage.
While hydrogen undoubtedly has an important role
in the future energy system, there should be some
caution about over expectations due to the rate of
scale-up required in production and the issue of
additionality. It is important to realize that the world
already uses vast quantities of hydrogen, almost all of
which currently comes from natural gas and coal.
These fossil fuels are heated to extract of hydrogen
while releasing CO2. About 115 million tons of this
" grey " and " brown " hydrogen is used to produce
fertilizers, plastics, and steel. Only about 40 thousand
tons of hydrogen is currently produced using
electrolysis. We therefore need about 3,000 times as
much hydrogen just to meet existing demand.
Creating complex and expensive ways to use green
hydrogen in new applications doesn't produce any
additional carbon reduction, if it could have been used
to replace grey or brown hydrogen, at no additional
cost. A massive ramp-up in both renewable energy
generation and electrolyzer production will be needed
to just to meet existing uses of hydrogen.
It is accepted that for very short range air-taxi-type
services, battery electric will be used; for long-range,
drop-in replacement biofuels and e-fuels will be used.
What is not so clear at this stage is where, in the
short- and medium-range flights, it will be optimal to
use battery, hydrogen, and SAF. n
ABOUT THE AUTHOr
Dr. Jody E. Muelaner is a chartered mechanical engineer with a
background in metrology, aerospace manufacturing, and machine
design. He now specializes in writing about technical topics in a way
that the target audience can easily understand. In 2018, he founded
Muelaner Engineering, Ltd. to provide consultancy and technical
writing services within advanced manufacturing and sustainable
transport. To date, he has authored 17 SAE EDGE Research Reports.
UPDATE
https://www.muelaner.com/
SAE Update - February 2024

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