Climate friendly propulsion technologies - Part 1 

While public pressure forces the aviation industry to significantly reduce its carbon footprint, the industry itself also has set itself ambitious goals for decarbonization. Most major airports around the world committed themselves to NetZero. In addition, organizations such as ICAO and IATA pledged to drastically reduce the industry’s carbon footprint.

To meet these challenging targets, there is an increasing need to develop – and certify - new propulsion technologies. Kerosene, which is practically the only means of propulsion in aviation today, is almost entirely derived from fossil sources, and thus is a major carbon emitter. The industry needs alternative, carbon neutral propulsion technologies, such as

• Hydrogen and 
• Electric propulsion.

Yet, the development of such technologies takes a significant amount of time. Not only must these technologies be developed and certified, but also new aircraft need to be designed for such types of propulsion. Certification procedures for these new types of aircraft can take up to 10-15 years. Timelines for electric and hydrogen flying in notable scales reach to 2035 and beyond.

Thus, it is a challenging task for airlines as well as airports, to meet regulatory requirements and self-imposed targets. 

As SAF has a different chemical composition that conventional jet fuel, it must be blended with regular fuel, the so-called drop-in. This ensures all critical specifications for safe operations in aircraft systems are met and the standards set by ASTM D1655 are fulfilled. The blend ratio can vary in this context, currently regulatory bodies such as EASA and FAA have approved blend ratios up to 50 %. A 100 % SAF use in commercial aviation is currently still being researched with first commercial flights already powered by 100 % SAF. The unknown in this matter is still the long-term impacts of Sustainable Aviation Fuels on jet engines and especially its gaskets.

Blended fuel also ensures compatibility with existing infrastructure, which does not have to be modified for SAF.

As production of SAF today is still relatively expensive and thus limited, blending SAF with conventional jet fuel helps gradually increasing the share of SAF under economic considerations. Eventually, production figures will have to be ramped up. 

Once a Sustainable Aviation Fuel is certified as aviation turbine fuel according to ASTM D1655, it is allowed to be dropped-in conventional jet kerosene. Thus, it can be handled in the same way conventional fuel is handled, no alternations need to be made to the existing fueling infrastructure. Airports need to monitor the fuel farms, though, and ensure that certified drop-in rates are not exceeded. 

Sustainable Aviation Fuels have the potential to significantly reduce carbon emissions in aviation, helping airports and airlines alike to meet regulatory obligations and fulfill their self-imposed sustainability commitments. Ongoing research and technological advances will further improve efficiency, scalability, and cost-effectiveness of such fuels. The largest impact on the industry’s carbon footprint will only be made through completely emission-free propulsion technologies, such as electric or hydrogen flying, but the development of these technologies still will take a significant amount of time and require investments in R&D, acquisition and infrastructure.

Until these technologies are available for wide-scale application, Sustainable Aviation Fuels represent an alternative propulsion technology that will make a significant contribution to reducing emissions and pave the way to carbon neutral flying. In addition, SAFs offer the advantage of being easy to use with existing fueling infrastructure and aircraft. Hydrogen or electric flying alternatives, on the other hand, require new types of aircraft, and a comprehensive charging respectively fueling infrastructure, which first has to be developed and certified.