Green Chile Chapter 691
of the Experimental Aircraft Association

Education and support for general aviation

Sustainable Aviation

Recently, my sister, who lives in Wyoming, home of the -70 degree wind chill factor, gave me a shellacking regarding my ignorance about biofuels.  In one of our normal telephone calls where we talk about family, politics, and how to solve the world’s problems, she happened to mention that biofuels looked promising for commercial aviation, and asked what did I think about that.  I said carbon is carbon, and it didn’t much matter if it came from plants and vegetables or dead dinosaurs; it makes CO2 when it burns. Then she laughed that little laugh that she uses when I say something dumb and explained to me that adding a renewable biofuel to jet fuel could significantly reduce net carbon emissions. She explained that with biofuels you basically recycle the CO2 instead of pulling more of it out of the ground.  I hadn’t really thought about that, but I argued it couldn’t be very efficient.  Then she told me that efficiencies up to 80% were possible.  I was starting to feel like a one armed man in a fist fight.  So I decided to do a little research on my own, and sure enough you can mix regular jet fuel with biofuel and the engines will keep running. In fact some airlines are already doing it on commercial flights and plan to do a lot more of it in the future to reduce their carbon emissions.

The amount of Sustainable Aviation Fuel (SAF) has tripled in 2022 compared with last year.

But the stuff isn’t cheap, at least not right now. In 2020 the price of SAF was over double that of regular jet fuel. Proponents of SAF claim that scaling production up and continued research and development will reduce the price of SAF. The cost of biofuels used in SAF can be reduced by using feedstock from waste streams that come from the food industry, agriculture, forestry, and even algae, and conversion efficiencies can be as high as 90%. The airlines are also being incentivized to use SAF to meet their carbon reduction goals. Meanwhile the cost of regular jet fuel continues to rise at 1% per year according to CFM International, a major engine manufacturer.

I wanted to get a better handle on cost and the practicality of using SAF to replace regular jet fuel, so I got ahold of my brother-in-law, who is a pretty smart guy. Not only does he run a refinery for an oil company, but he also had his own little biofuel processing plant in the back yard. Through some chemical engineering magic he turned McDonalds french fry grease into something that his diesel truck engine would happily run on. So I figure he knows a thing or two about both petroleum and bio fuels. He told me that petroleum and bio fuel costs are both driven by supply and demand. If the airlines start buying a lot of biofuel, its price is more likely to go up than down until they find a cheaper way to make it, and the companies that produce it can ramp up production. He also said that the biodiesel fuel he was making had a higher freezing temperature than regular diesel fuel, so he had to mix the two together to keep it from freezing in the winter. It has something to do with long carbon chain molecules in biofuels versus shorter ones in petroleum fuels. That is one of the reasons why they use a blend of biofuel to regular fuel in SAF. SAFs are currently approved for blends from 10% to 50%.

By the time I got off the phone with my brother-in-law it was clear to me that the development and use of SAF to replace jet fuel wasn’t going to be all unicorns and pixie dust. On the other hand, it has the potential to become cost effective in the future, and it can certainly begin to reduce the commercial aviation’s carbon footprint right now. That is a start at least. I should call my sister and brother-in-law more often. I could learn a lot from them:-)

Biofuels like Sustainable Aviation Fuel (SAF) can be made from things such as used cooking oil, forestry waste, and even algae.  It is currently blended with traditional jet fuel for use in aircraft.  SAF can reduce carbon emissions by up to 80% compared to the fuel it replaces.