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[[Specific energy]] is an important criterion in selecting fuel for an aircraft. The much higher [[energy storage]] capability of hydrocarbon fuels compared to batteries has so far prevented [[electric aircraft]] using [[electric batteries]] as the main propulsion energy store becoming viable for even small personal aircraft.
As aviation moves into the renewables era, [[hydrogen-powered aircraft]] might enter common use.
|doi=10.1063/PT.3.4632▼
|title=Hydrogen-powered aircraft may be getting a lift ▼
|last1=Kramer ▼
|first1=David▼
|author-link=▼
|date=1 December 2020 ▼
|journal=[[Physics Today]]▼
|volume=73 ▼
|issue=12 ▼
|pages=27–29 ▼
|bibcode=2020PhT....73l..27K ▼
|doi-access=free}}</ref> With materials available in the 2020s, the mass of tanks strong enough to withstand this kind of high pressure will greatly outweigh the hydrogen fuel itself, largely negating the weight to energy advantage of hydrogen fuel over hydrocarbon fuels. Hydrogen has a severe volumetric disadvantage relative to hydrocarbon fuels, but future [[blended wing body]] aircraft designs might be able to accommodate this extra volume without greatly expanding the [[wetted area]].▼
Even if finally practical, the industry timeline for adopting hydrogen is fairly lengthy. Alternatives to conventional aviation fuel available in the near term include [[aviation biofuel]] and synthetically created fuel (aka "e-jet"). These fuels are collectively referred to as "Sustainable Aviation Fuel" (SAF).▼
==Types of aviation fuel==
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{{Main|Natural_gas#Transportation}}
[[Compressed natural gas]] (CNG) and [[Liquefied natural gas#Transportation|liquified natural gas]] (LNG) are fuel feedstocks that aircraft may use in the future. Studies have been done on the feasibility of using natural gas<ref>{{cite web|url=http://lae.mit.edu/aircraft-design/|title=Aircraft Design - MIT Laboratory for Aviation and the Environment|access-date=27 December 2016|url-status=dead|archive-url=https://web.archive.org/web/20161230163921/http://lae.mit.edu/aircraft-design/|archive-date=2016-12-30}}</ref> and include the "SUGAR Freeze" aircraft under NASA's N+4 Advanced Concept Development program (made by Boeing's Subsonic Ultra Green Aircraft Research (SUGAR) team). The [[Tupolev Tu-155]] was an alternative fuel testbed which was fuelled on LNG.<ref>{{cite web|url=http://midwestenergynews.com/2013/08/26/could-natural-gas-fuel-commercial-flights-of-the-future/|title=Could natural gas fuel commercial flights of the future?|last=EnergyWire|access-date=2016-12-27|url-status=live|archive-url=https://web.archive.org/web/20161105204049/http://midwestenergynews.com/2013/08/26/could-natural-gas-fuel-commercial-flights-of-the-future/|archive-date=2016-11-05}}</ref> The low specific energy of natural gas even in liquid form compared to conventional fuels gives it a distinct disadvantage for flight applications.{{citation needed|date=March 2018}}
==== Liquid hydrogen ====
Hydrogen can be used largely free of [[carbon emission]]s, if it is produced with power from [[renewable energy]] like [[wind power|wind]] and [[solar power]].
Hydrogen fuel cells do not produce {{CO2}} or other emissions (besides water). However, hydrogen combustion does produce {{NOx}} emissions. Cryogenic hydrogen can be used as a liquid at temperatures below 20 K. Gaseous hydrogen involves pressurized tanks at 250–350 bar.<ref name=Kramer2020>{{cite journal
▲ |doi=10.1063/PT.3.4632
▲ |title=Hydrogen-powered aircraft may be getting a lift
▲ |last1=Kramer
▲ |first1=David
▲ |author-link=
▲ |date=1 December 2020
▲ |journal=[[Physics Today]]
▲|volume=73
▲ |issue=12
▲ |pages=27–29
▲ |bibcode=2020PhT....73l..27K
▲ |doi-access=free}}</ref> With materials available in the 2020s, the mass of tanks strong enough to withstand this kind of high pressure will greatly outweigh the hydrogen fuel itself, largely negating the weight to energy advantage of hydrogen fuel over hydrocarbon fuels. Hydrogen has a severe volumetric disadvantage relative to hydrocarbon fuels, but future [[blended wing body]] aircraft designs might be able to accommodate this extra volume without greatly expanding the [[wetted area]].
▲Even if finally practical, the industry timeline for adopting hydrogen is fairly lengthy. Alternatives to conventional aviation fuel available in the near term include [[aviation biofuel]] and synthetically created fuel (aka "e-jet"). These fuels are collectively referred to as "Sustainable Aviation Fuel" (SAF).
==Production of aviation fuel==
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