As airlines across the globe are confronting the climate crisis, aircraft are quickly changing to address the need for environmental consciousness. In the pursuit of sustainability, the International Civil Aviation Organization (ICAO) set the goal to transition the aviation industry to carbon neutrality by 2050, amounting to the reduction of nearly 1 gigatons of CO2. Reaching this goal will require the use of alternative fuel sources such as sustainable aviation fuel and electric aircraft. There is also the potential change of fuel required for the general aviation aircraft used for flight training, as there is increasing political pressure to police the presence of lead-based fuels. While these changes are impending, questions remain about the downstream effect of these changes on how aircraft will fly. Jekaterina Shalopanova, Chief Business Officer of Aerviva, explains this next generation of fuels, and provides insight into how the changes will affect the task of flying.
Sustainable Aviation Fuel
“Sustainable aviation fuel has emerged as a clear frontrunner for the industry’s change to carbon neutrality,” Shalopanova said. “However, luckily those in the industry who use Jet-A, SAF will be a ‘drop-in’ solution for climate responsibility, and for the most part will be indistinguishable from the fuel blends we use today.”
According to McKinsey & Company, around 4.5 Megatons of SAF will be demanded by 2030. Unlike Jet-A, which is a refined kerosene gas originating from petroleum, SAF uses feedstocks such plants, waste, cooking oil, and a variety of other naturally occurring sources. On a chemical level, SAF uses the same hydrocarbons that have been present in Jet-A for years, complying with widely acceptable jet fueling standards such as EI/JIG-1530, JIG1, JIG2, ATA103. Engine manufacturers such as Pratt & Whitney report that more than 450,000 commercial flights have already operated with SAF in 2022 on airlines such as Air France-KLM, Lufthansa, DHL, Delta, United, and others, while GE says that their most popular jet engines such as the CFM-56 that powers the 737 and A320 are SAF ready.
“For these flights, crews and aircraft function on identical procedures and experiences as the weight of the fuel remains the same, and the solution is ‘drop-in,’ requiring no major change,” Shalopanova said. “The fuels will have different energy density which changes how the injection and combustion systems of engines work, and SAF doesn’t include important aromatics that help prevent fuel leaks, however engine manufacturers are confident their engines will run them and the results of these tests will likely remain industry secret for some time.”
Beyond the change of SAF for pilots, Aviation Week has reported that the certain blends of SAF from hydro processed esters and fatty acids have up to 90% less sulfur, which improves lubricity and cleanliness of the engine, potentially meaning engines will become less expensive to maintain. Shalopanova explains that the largest change could be from how the fluid interacts with the aircraft’s fuel lines.
“The most radical hypothetical will be an increased importance on fuel flow monitoring as the cavitation properties, bubble nucleation rates, and shock transformation of SAF can potentially produce fuel leaks before aircraft design is changed to operate with high SAF blends,” Shalopanova said. “While engine manufacturers say that their engines are ready, the lack of energy density can alter fuel pump performance during extreme temperatures and high climb rates, affecting total available power on take-off and requiring more conservative performance from both aircraft and pilot.”
Unleaded aviation fuel
Recent years have seen a very fast and well supported push to remove lead from aviation fuel used to power piston driven aircraft. The European Union passed laws in 2022 targeted at the reduction and restriction of the chemical Tetrathyllead used in aviation fuel in its member states, with similar bans being proposed in the United States and Great Britain. This is a significant and controversial action, as piston-driven general aviation aircraft used for flight training in Europe are powered by engines that depend on fuels that take advantage of Tetrathylead when producing the power necessary to fly. use lead. 100 octane low lead fuel, or ‘100LL’ or simply referred to as ‘AvGas’ in the industry, uses lead molecules to provide performance stability at high octane. At 100 octanes, lead reduces the explosive elements of fuel, making it a more stable source of the high power needed. In short, the presence of lead allows aircraft engines to get more power from more explosive fuel without the fuel becoming too explosive to operate.
“The change will have a large impact for general aviation operations; however, this has been a long time coming,” Shalopanova said. “While engine designers and aircraft manufacturers know that leaded fuel was going to eventually run into the challenge it faces now, its performance qualities have been hard to walk away from.”
The search for a replacement for 100LL gas has occurred for decades, and some engines have already been modified to accommodate a lack of lead. The challenge behind this fuel replacement is that alternative fuels that use ethanol are fundamentally incompatible with piston driven aircraft due to their hygroscopic nature, or ability to collect water. Water in aircraft engines produces dangerous lack of performance, and pilots are trained to inspect their fuel for water contamination before flight.
“So far, tested replacements for 100 low lead have proven they perform no differently, and aircraft engines in Europe have begun to use diesel fuel, Jet fuel, and car gasoline without ethanol since there isn’t much change in performance,” Shalopanova said. “Engine manufacturers have made the design changes to their platforms years ago in anticipation of this change so engines don’t experience valve deterioration when lead is removed.”
Shalopanova added that some piston-driven aircraft engines might experience slightly less available power as a direct result of the less power available in the lower octane fuel for common unleased gas, however the difference wouldn’t change aircraft performance significantly.
Electric and hydrogen aviation
“Alternative sources such as electric and hydrogen aviation still offer the most uncertainty,” Shalopanova said. “Hydrogen is a highly explosive fuel, so unlike other options its switch wouldn’t change performance, but dealing with cryogenic systems to operate the fuel might change procedure.”
While hydrogen and electric aircraft platforms have begun flight testing, the designers of early generation platforms are still years away from introduction into the market. Certain hydrogen manufacturers, such as ZeroAvia are trying building platforms that can be scaled to current aircraft in use, which implies a lack of substantial difference in the platform, while electric aircraft will face difficulties from lack of power and increased weight of batteries.
In conclusion, while it is known that aviation will become more sustainable in the next few years, the exact details of this change remain to be seen as there are many different blends of SAF as well as a few options for unleaded aviation fuel, and years before electric and hydrogen platforms are developed. What is known is that there is a need to change, and this need will be balanced with industry demand. Alternatives that are easy and familiar to use are likely to become more widely adopted along the timelines necessary for the climate crisis.
