March 27, 2020, ©. Leeham News: In this week’s Corner, we analyze the use of carbon-neutral fuels for airliner use.
Almost all variants of carbon-neutral fuels have the “drop-in” advantage, they can replace our regular jet fuel in a mixed capacity or entirely with none or minimal changes to our present aircraft and their engines.
It’s a big subject, and I will use the next Corners to explain the key alternatives, their production process, and what benefits and problems they bring.
The majority of carbon-neutral fuels are chemically similar enough to our airliner Jet A-1 fuel that they can be approved as a “drop-in” alternative. This means a recognized authority creates a fuel specification that is qualified for use in airliners by the aircraft OEMs and as long as fuel producers adhere to the specification the fuel can be used in the approved aircraft’s fuel systems.
The alternative fuel is approved either in a mix with a ratio of alternative fuel to Jet-A1 of up to typically 50% or as an outright replacement for Jet-A1.
The alternative fuels that are approved for use in our airliners today are bio-based fuels. Bio-based fuels are produced from biomass, bio fats and oils or other waste products. They are the alternative to fossil fuels in the short term for air transport. They been in development over the last decades and are in active use today with a handful of airports offering them as an alternative to the fossil Jet A-1 fuel for business aircraft and airliners.
We will discuss their production, cost, and adoption more in-depth in a subsequent Corner.
The alternative to bio-based fuels is synthetic fuels. A production process synthesizes the fuel’s hydrocarbons from CO or CO2 sources with gaseous hydrogen to form the jet fuel’s hydrocarbons.
The synthetic fuel process is energy-intensive and seems unattractive at first. If we could store produced energy efficiently, synthetic fuels would not be an alternative. But we can’t.
We have analyzed the problems of storing energy in a chemical process in our battery discussions. For large energy levels and long time storage, battery storage is unpractical.
The world’s renewable energy production, like hydroelectricity, wind, or solar energy, is often produced at places and at times when there is no local energy need. Synthetic fuel can then be seen as long time storage of energy from sources where there is no immediate local consumption.
Examples are remote geothermal, waterelectricity, wind, or sun energy production. The windiest parts of the planet are the open seas where no energy consumption takes place, the sunniest places the deserts where no people concentrations are. And so forth.
Seen in this perspective, synthetic fuel production can be a rational way to use the natural sources of renewable energy the globe offers. By nature of a more complex total solution, synthetic fuels are a longer-term carbon-neutral fuel alternative.
Airliner approved bio-fuels exist and are used today. We will look deeper into these in the next Corner.