Clean Fuel: The Future of Aviation

One day, planes will fly without using gasoline and instead on a steady diet of fats, starches, sugars, trash… along with other exotic fuels. That’s the plan of American, Delta and United, which have all set ambitious goals to reduce their carbon emissions by 2050.

General trend

Last year, Virgin Atlantic successfully completed a transatlantic flight powered entirely by synthetic fuels made from plant fats and sugars. This development opens up a future for sustainable aviation fuels (SAF). SAF is a generic term for aviation fuels that emit less carbon than conventional jet fuel, produced from resources such as bio-based oils, agricultural by-products, etc.

Virgin Atlantic has received permission from the UK Civil Aviation Authority to operate a long-term transatlantic flight using 100% sustainable aviation fuel (SAF). Photo: VIRGIN ATLANTIC

The Boeing 787 used by Virgin Atlantic on the flight used SAF, which has 70% less carbon emissions than synthetic jet fuel from petroleum. Previously, an Airbus A380 passenger plane also tested a 3-hour flight using fuel made mainly from cooking oil and waste grease. To date, no one has designed a battery that is light enough but also powerful enough to power a commercial aircraft. Therefore, the most practical way to reduce emissions in the aviation industry is to require aircraft to use SAF.

Reducing the carbon footprint of aircraft will depend on sourcing, however, as none of the potential sources will meet all of the fuel demand. Although the Biden administration has set a goal of sourcing 100% sustainable aviation fuel by 2050, the US produced enough sustainable fuel last year to meet less than 0.2% of the fuel consumption of the US aviation industry.

Sourcing

Nearly all sustainable jet fuel to date is made from some form of fat, including used cooking oil, vegetable oils, and animal fats, but supply falls short of demand. The United States and Europe currently use nearly all of their domestic supply of used cooking oil, and import additional waste fats from Asia to produce biofuel for planes, cars, and trucks.

The next wave of sustainable jet fuels to hit the U.S. market in the coming months could be made from corn and sugarcane. Previously, refineries fermented the starch and sugars in these crops into ethanol, which was then blended into gasoline and diesel. Alternative fuel startup LanzaJet has opened the world’s first plant to produce jet fuel using ethanol made from American corn, Brazilian sugarcane, and more.

One drawback is that fuels made from food crops may not be as sustainable as fuels made from waste. Agricultural land is limited, and expanding biofuel crop acreage could have negative environmental consequences, such as excessive water use and deforestation, releasing more carbon into the atmosphere. To meet the entire US aviation fuel demand with corn ethanol, the country would have to grow 114 million acres of corn—an area larger than the state of California. This is why European regulations do not consider most biofuels made from food crops to be “sustainable,” and jet fuel made from corn ethanol may not qualify for tax incentives under the US definition, according to the Washington Post.

As an alternative, producers are developing methods to produce jet fuel from cellulosic cover crops, a type of grass that is often grown on farms between regular growing seasons to keep the soil healthy. Because these plants grow off-season, they don’t compete with food crops for farmland, making them more sustainable.

Several companies are turning waste into jet fuel. One is the US refinery Fulcrum Bioenergy, which is set to open a waste-to-fuel plant in 2022. But not all waste is good feedstock; it needs to be sorted. Other forms of waste are more suitable, such as agricultural waste, including stems, leaves and unpicked produce, or husks and hulls left over from food processing. Tree branches and bark left over from logging, sawdust and wood chips can also be sources of fuel. Green hydrogen fuel is also being considered.

While the production of jet fuel from hydrogen is still in its infancy, once production begins to ramp up, green hydrogen will quickly become one of the largest sources of sustainable fuel, predicts SkyNRG, a sustainable aviation fuel producer.

KHANH HUNG

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