By Li Qiao
The One Big Beautiful Bill Act, a federal spending law passed in early July 2025, drastically cuts federal funding for initiatives to develop sustainable or renewable fuels that can power airplanes over long distances while reducing the harm aviation causes to the environment.
About 2.5 percent of the world’s carbon emissions in 2023 came from aviation. Because there aren’t many options for large, portable amounts of energy-dense fuel, reducing emissions from airplanes is especially challenging. For example, airplane fuel tanks would be much smaller and lighter than electric batteries that might power an international flight.
As an aeronautical engineer, one possible remedy is a type of fuel known as sustainable aviation fuel. Sustainable aviation fuels are made from renewable and waste resources such used cooking oil, leftover agricultural material, algae, sewage, and trash, in contrast to traditional jet fuel, which is refined from petroleum. However, they are sufficiently comparable to traditional jet fuels to function in current aircraft engines and tanks without requiring significant changes.
The U.S. government had set some ambitious goals before Donald Trump’s second term as president: producing three billion gallons of this kind of fuel annually by 2030 and enough to power every commercial aircraft travel in the country by 2050. However, the trip ahead is lengthy.
A range of source materials
Early attempts to develop sustainable aviation fuels focused on food crops, such as soybean oil being converted into biodiesel or corn into ethanol. Although the basic ingredients were easily accessible, cultivating them put food production in competition.
Nonfood sources like algae or agricultural waste like manure or maize stalks are being used to create the next generation of biofuels. Food supplies are not in competition with these. They may also reduce carbon emissions if handled effectively because algae absorb carbon dioxide while growing and using agricultural waste prevents greenhouse gas emissions from decomposing.
Due in part to the new technology and in part to the lack of logistics capabilities for the collection, transportation, and processing of vast amounts of source material, these biofuels are more costly and more difficult to generate.
Using genetically modified microorganisms that transform particular raw materials into biofuel, some researchers are attempting to produce biofuels. One approach involves growing algae to produce sugars or oils, which are then fed to microbes that have been designed to convert them into fuels like ethanol, butanol, or oralkanes. Another attempt is to modify photosynthetic microorganisms, such cyanobacteria, so they can directly turn carbon dioxide and sunlight into fuel.
The goal of all these strategies—as well as others under investigation—is to develop carbon-neutral, sustainable substitutes for fossil fuels. Despite how exciting it sounds, the majority of this technology is still only accessible in labs and not at airports.
Blends are being tested
Currently, airlines are permitted by the U.S. Federal Aviation Administration to use mixes of up to 50% sustainable aviation fuel in addition to regular jet fuel to power their aircraft. The precise amount is determined by the fuel’s manufacturing process, which includes how chemically and physically comparable it is to jet fuel derived from petroleum and, consequently, how well it will function in the tanks, pipelines, and engines of an aircraft that is already in place.
Cost and supply are the two main obstacles to broader adoption. The cost of sustainable fuels is significantly higher than that of conventional jet fuel, with variations depending on the raw material and technique. For example, one form of sustainable fuel sold for around $5.20 per gallon in 2024, whereas the most popular petroleum-based aviation fuel, Jet-A, had a raw price of US$2.34 per gallon on average.
The cost of producing these fuels is essentially increased by the reduction of government subsidies in the July 2025 federal budget.
Sustainable fuel is only produced in tiny amounts due in part to its high cost; global production is projected to reach around 2 million metric tons in 2025, or less than 1% of the global demand for aviation fuel. Beginning in January 2025, all jet fuel supplied at airports in the European Union must include at least 2% sustainable fuel, with minimum percentages rising over time, due to pressure from throughout the world to raise demand.
Planes can use these fuels
Businesses like General Electric and Rolls-Royce have demonstrated that their aircraft engines can operate flawlessly on sustainable fuels.
Nonetheless, the density and energy content of sustainable aviation fuels may differ slightly from that of conventional jet fuel. This implies that the weight distribution and flight range of the aircraft may alter.
Additionally, other components of the aircraft, like those that store, pump, and maintain fuel balance, must work together. This covers rubber seals, pipes, and valves. I discovered that Boeing and other aircraft manufacturers are collaborating closely with their suppliers to guarantee that sustainable aviation fuels may be securely and dependably incorporated into every component of the aircraft during my summer 2024 visit as a visiting lecturer.
You may have heard headlines about flights using 100% sustainable aviation fuel, but those headlines don’t tell the whole picture because of those finer subtleties. Typically, a small quantity of regular jet fuel or unique additives are present in the fuel used on those flights. The reason for this is because certain of the aromatic chemical compounds needed to maintain appropriate seals throughout the aircraft’s fuel system are absent from sustainable fuels compared to fossil-based fuels.
Good promise, with work ahead
Sustainable aviation fuels present a viable means of lowering the carbon footprint of air travel without completely redesigning or reinventing aircraft, while there are still many unanswered questions. By drastically reducing carbon dioxide emissions from currently operating airplanes, these fuels can lessen the impact of climate change.
Whether or not the United States is involved, the project will require research and funding from governments, manufacturers, and airlines worldwide. However, the fuel that powers your aircraft might be far more environmentally friendly in the future than it is now.
At Purdue University, Li Qiao teaches aeronautics and astronomy.
