Future Aircraft Need Sustainable Aviation Fuels

Few days remain where commercial airliners pull up to an airport gate to deplane passengers while the ground crew adds standard jet fuel, readying the aircraft to fly to the next destination. Nations are regulating aviation CO2 emissions and calling for significant reductions of those emissions by 2050—no matter how efficient the aircraft engine is, standard jet fuel needs to change.  

Standard jet fuel is known as Jet A or Jet 1—a readily available, kerosene-based formulation designed to burn in all commercial jet aircraft engines. The fuel consumed by the commercial aviation industry produces about 2% of global CO2 emissions, and these emissions are estimated to triple by 2050. There are only two viable options for replacement fuel: low emission or net-zero emission fuel.  

Today, different versions of sustainable aviation fuel (SAF) are in use. Produced from renewable feedstocks, SAF is considered a drop-in fuel, meeting the same technical and safety requirements of fossil fuels. SAF burns the same hydrocarbons as fossil fuels and produces comparable emissions, but it comes from more sustainable sources. The sustainable sources and production process of SAF result in a net reduction of emissions over the fuel lifecycle compared with fossil fuels. Unfortunately, SAF production has not risen to the levels needed to make a significant contribution to reducing CO2 emissions. In 2019, SAF production accounted for less than 1% of total jet fuel demand. 

Other Fuel Options Require Significant Improvements

Other fuels are available to commercial aircraft, but these options are not ready to disrupt Jet A, and they aren’t yet able to power a large passenger aircraft safely and economically. Although hydrogen- and electric-powered aircraft have flown, neither is ready to become a primary alternative for mass adoption. 

The industry is exploring hydrogen fuel as the next iteration of renewable fuel. Hydrogen has many benefits including availability, energy density, and a decades-long history of use as a primary aviation fuel—including military prototypes in the 1950s. Hydrogen is efficient, and engines can be easily adapted to use the fuel. However, like other fuels, there are negatives to its use. To have enough hydrogen fuel to last a flight, it must be compressed or liquified. This requires an aircraft to have large storage tanks to hold enough compressed hydrogen for long-distance flights, which presents drawbacks for passengers and cargo capacity. Also, when hydrogen is liquified, it drops to -253°C (−423°F), requiring storage in insulated tanks to maintain temperature and reduce evaporation. Neither of these options is ideal for passenger aircraft. 

Small electric-powered aircraft are in service today, ferrying passengers on aircraft originally built to use liquid fuels. The largest of these aircraft, the eCaravan, carries up to nine passengers with a 100-mile range, far from the size and range that will be required in the future. To carry those nine passengers, the eCaravan is equipped with more than 2,000 lbs of lithium ion batteries. Companies are designing and testing larger electric aircraft, but their passenger capacity, range, and size are greatly affected by the weight and capacity of current batteries.

These fuels will someday be viable replacements for Jet A, but only after significant improvements are made in each. For now, Jet A will be prominent until SAF production increases enough to make a difference, with adoption of hydrogen or electric-powered aircraft likely in 2030 or later.