Sustainable aviation fuels (SAF) are a breakthrough in our competing desires to fly far and fast, all while lowering our carbon footprint. Despite the fact that the Honeywell TPE331 is an incredibly efficient engine, it’s clear the world is ready to move on from the environmental impact caused by conventional jet fuel.
First introduced more than a decade ago, SAF has rapidly progressed into a promising replacement for petroleum-based jet fuel. It was originally dubbed biofuel, but the increasing variety of raw source materials spawned a more inclusive marketing term. Today SAF can be produced by an astounding array of organic and inorganic materials. Municipal solid waste, including product packaging, grass clippings, furniture, and bottles, has great potential because of its vast supply. Cellulose waste, such as excess wood and forestry products, has already been proven as technically viable and marketable, as has used cooking oil. Crops such as jatropha and camelina have high fat contents, making for great fuel sources, although with the typical downsides of using agricultural land for fuel production. Other processes that show potential, but aren’t yet economically viable, include algae and something called power-to-liquid. This process takes energy produced from renewable sources, water, and carbon dioxide from the air, and converts it to fuel. It’s like hitting the reverse button on the fuel burning process.
Each SAF production method has environmental advantages and disadvantages, and some have the potential to reduce aviation’s greenhouse gas emissions by 80 percent. With commercial aviation’s commitment to cap carbon dioxide emissions at 2020 levels, and halve emissions from 2005 levels by 2050, only SAF seems to have the current mix of easy swap-in, economics, and environmental benefits.
Currently all available SAF is drop-in approved, meaning it doesn’t require any approvals, paperwork, flight planning changes, or documentation. While it is likely to change in the future, today SAF is blended with traditional jet fuel at concentrations between 10 and 50 percent, and meets the same chemical composition specifications as full petroleum-based Jet A. Although it doesn’t happen in practice, theoretically an FBO could offer SAF without the pilot even knowing it was being dispensed.
Recently Honeywell announced it had tested full SAF on an HTF7500 with good results, and it’s conceivable that 100-percent SAF will work for other engines as well. But to this point, ASTM, the organization that sets the chemical standards for jet fuel and avgas, has given expedited pathways for any blend up to 50 percent. Beyond that will take significantly more time and investment to study, certify, and distribute.
As companies look for ways to make environmental goals, SAF demand should steadily increase. Aviation organizations, government, and aircraft manufacturers are starting to coalesce around a future where SAF is a dominant fuel. Every jet that comes out of Gulfstream’s Savannah facility goes to the buyer with a load of SAF, as do the jets from Cessna.
