Technology
It is currently unclear which propulsion and fuel technology or combinations of technologies will enable aviation to move beyond carbon. This page provides an overview of these competing technologies, their advantages and their drawbacks.
New Engine and Fuel Technology
Electric Engines Powered by Batteries
Electric engine powered by electricity chemically stored in a battery. So long as the battery has been charge with electricity from a renewable source, this completely removes all GHGs from aviation. Not only CO2 but NOx and water vapor, in addition to other by products with GWP. It has the further benefit of radically reducing noise pollution. However battery powered electric engines have a major drag back with their power density. Currently only small planes flying few people short distances are possible. But this is a rapidly evolving technology causing a lot of excitement and generating serious investment.
Advantages
- Battery powered flight offer true decarbonized flight – so long as the batteries are charged with electricity produced from a renewable source
- Electric power eliminates all other GHGs currently produced by a jet engines
- Electric engines produce far less noise than jet engines, resolving a major headache for people who live under the flight path of busy airport – the knock effect of this is it would allow congested airports (such as Heathrow) to dramatically increase capacity by operating overnight, rather than building additional runaways
Disadvantages
- Power density of current battery technology is currently many times less than what is required to fly the payload of a commercial aircraft any meaningful distance
- There are doubt about how long it could take for battery technology to reach a sufficient density for commercial aviation, and it may never do so for long haul flights
Electric Engines Powered by Hydrogen Fuel Cells
This solution would most likely use similar engine and blade technology as engines powered by lithium-ion type battery technology but the fuel source would be a hydrogen fuel cell in place of battery.
Advantages
- Battery powered flight offer true decarbonized flight – so long as the batteries are charged with electricity produced from a renewable source
- Electric power eliminates all other GHGs currently produced by a jet engines
- Electric engines produce far less noise than jet engines, resolving a major headache for people who live under the flight path of busy airport – the knock effect of this is it would allow congested airports (such as Heathrow) to dramatically increase capacity by operating overnight, rather than building additional runaways
Disadvantages
- Power density of current battery technology is currently many times less than what is required to fly the payload of a commercial aircraft any meaningful distance
- There are doubt about how long it could take for battery technology to reach a sufficient density for commercial aviation, and it may never do so for long haul flights
New Fuels Using Current Engine Technology
Hydrogen Fuel
Hydrogen has been used in the past as the fuel for jet engines. The has a very high energy density solving the main issue of most alternatives to fossil fuel. The issues with hydrogen come from how to make it and how to store it and how to handle it. Storing the fuel in an aircraft’s wings, as is the case for all jet fueled aircraft would not be possible. It would need a far stronger fuel tank and would need to part of the fuselage, adding weight and volume or any aircraft.
Currently there is not way to economically produce hydrogen without emitted carbon in the process.
Advantages
- Hydrogen has a very high energy density by weight – 3 times that of jet fuel
- Hydrogen could be used in modified versions of current jet engine technology
Disadvantages
- Hydrogen is very difficult to store, options range from very heavy high pressure tanks to storing it as a super-cooled liquid at extremely low temperatures
- These properties would make fuel tanks very heavy and make refueling extremely challenging
- Hydrogen produces water valor when it is burnt, which, when emitted high in the atmosphere contributes to global warming
- There are many ways to make hydrogen, the cheapest ways produce a lot of carbon, the cleanest ways are very expensive
Sustainable Aviation Fuel
Sustainable Aviation Fuel is a replacement for standard jet fuel, but it is made with a sustainable feedstock. It is estimated that replacing jet fuel with SAF reduces carbon emission by about 80% over the lifecycle of the fuel. Feedstocks for SAF can be used cooking oil or household waste (MSW). Producers and end-users (airlines) usually stipulate that the feedstock cannot be palm oil or anything else that competes with land or other natural resources with food or forests or other existing uses that are beneficial to the environment. SAF’s big advantage is that it can be used with existing jet engines and fuel transportation infrastructure, making it the only method, that is currently technically viable, of drastically reducing carbon emissions. Currently, according to the relevant regulation in the US (ASTM D7566) a blend of up to 50% of SAF can use mixed with standard jet fuel and used for commercial flights. United and KLM are two major airlines that have started to use SAF but at levels at or below 1%. The cost and the supply remain serious challenges to its widespread use.
Advantages
- SAF offers a technically viable method or drastically reducing the aviation industry’s dependence on traditional hydrocarbon jet fuels
- Given the development, testing, certifying and manufacturing timeline projected for zero carbon propulsion methods, SAF appears it may be the only path to radically reducing carbon emission from medium and long haul flight
Disadvantages
- Cost of producing SAF is far greater than hydrocarbon jet fuel
- An adequate feedstock for manufacturing SAF has yet to be determined
- Serious capital investment would be required to produce enough SAF for the aviation industry
Carbon Offsetting
No changes are made to the current technology fuel or propulsion method, but carbon produced is offset by the carbon producer paying to for carbon reductions in another activity, or by paying for a carbon sink, such as the planting trees. This is example of a market based measure of net carbon reduction. Carbon offsets can bought and sold through the credit for carbon credits.
Advantages
Disadvantages
- This is the only solution that has zero dependence on technological advances, everything we need to offset every ton of carbon produced by the aviation industry currently exists
- May be the only viable option for long-haul flights for the medium term, given the scale of advances required in the power density of new technologies such as battery or hydrogen power electric aircraft
- Carbon markets such as the EU’s ETS (Emissions Trading Scheme) have existed for years, and should be become more robust over time and as more countries join
- Price of carbon credits have been highly volatile making it difficult for companies to budget the cost of offsetting carbon
- Carbon has no intrinic value, the market and price of it has to be created through legislation in each country – many countries will inevitable refuse to participate
- Verification of carbon offset schemes can be difficult, some have a questionable impact on the environment, trees may be planted where there was already natural vegetation, programs may encourage monocultures which damage natural bio-diversity
Carbon Free Aviation Video Learning Center
Warning: the YouTube rabbit hole starts here…
Please note, Carbon Free Aviation holds no copyright over these videos, they are posted here for the furtherance of knowledge in the field of Carbon Free Aviation, and the betterment of mankind.
Flight Global’s Sustainability Webinar
Posted: 12 Feb 2021
Flight Global leads a discussion on the feasibility of migrating to sustainable propulsion in the coming years.
AERO 2020 – e- Online Panel Discussion # 1 Electric Propulsion Unit (EPU) and certification
Posted: 4 Apr 2020
This video provides a highly technical overview on the state of development from some of the major players in the electrical aviation industry