A new Boeing ecoDemonstrator flight-test program to measure how sustainable aviation fuels (SAFs) affect non-CO2 emissions will add further data to previous studies which have suggested that cleaner-burning jet fuels could produce up to 70% fewer planet-warming contrails.
Contrails are formed in certain atmospheric conditions when water vapor from jet engines condenses and freezes around soot particles, leaving a trail that is visible from the ground. Over time, longer-lasting contrails can merge together to form heat-trapping contrail-cirrus clouds, which contribute to global warming.
While the spotlight on aviation’s environmental impact focuses primarily on carbon-dioxide emissions, it is thought that non-CO2 aircraft emissions could account for as much as two-thirds of the industry’s contribution to climate change.
Given that the International Air Transport Association (IATA) sees SAF as potentially accounting for 65% of the abatement needed for the aviation industry to meet its goal of achieving net zero carbon emissions by 2050, it would be welcome news for the sector if these fuels could also reduce the non-CO2 effects of flying.
Boeing announced earlier this month that it is working with NASA and United Airlines to test the effects of SAF on non-CO2 emissions, using an ecoDemonstrator Explorer 737-10 aircraft. The three-week campaign is being supported by the US Federal Aviation Administration (FAA), GE Aerospace and the German Aerospace Center (DLR).
The jet will fly with 100% SAF, provided by Paramount, California-based World Energy, in one tank and conventional jet fuel in the other. The SAF is derived from renewable biomass feedstocks, including agricultural waste, fats and oils.
The test aircraft will be trailed by NASA’s DC-8 airborne science lab aircraft, which will measure emissions produced by each type of fuel and examine any resulting contrail ice particles. In addition, NASA satellites will capture images of contrail formation as part of the test.
“Flight testing is complex and resource-intensive, yet it’s the gold standard for understanding how sustainable aerospace innovations affect changes in contrails and climate,” says Rich Wahls, NASA mission integration manager for the Sustainable Flight National Partnership. “This is why we’re bringing NASA’s DC-8 to bear on this collaboration, where the valuable flight data will improve our predictive models.”
In air-to-air testing, NASA’s DC-8 Airborne Science Lab will fly behind the Boeing ecoDemonstrator Explorer to measure emissions and contrail ice particles. (Image: NASA)
United’s chief sustainability officer, Lauren Riley, adds: “This collaboration between Boeing, NASA and United has the potential to not only help us better understand contrails, but to provide the full scope of what our transition to SAF can provide beyond greenhouse-gas reductions.”
Boeing and NASA have previously conducted ground testing of SAF emissions in 2021 on an Alaska Airlines 737-9 ecoDemonstrator and in 2022 on a 777-200ER ecoDemonstrator. The airframer says the data from these earlier tests confirmed that the use of paraffinic SAF yields “dramatic particle emission reductions”.
NASA and DLR have also previously worked together to study whether the use of SAF can reduce contrails. Research conducted by the two organizations in 2021 using an Airbus A320 found that burning SAF could result in 50-70% fewer ice crystal contrails at cruising altitude than conventional jet fuel. This is because the engines released fewer soot particles when burning SAF. While the ice crystals that were formed were larger in size, researchers reported that they fell more quickly and melted in the warmer air below.
Detailing the findings at the time, Richard Moore, a NASA scientist at Langley Research Center in Virginia, said: “We know that contrail formation from jet exhaust has a larger, more immediate impact on climate than carbon dioxide emissions. This research shows that we have an opportunity using alternative fuels to make immediate changes that could help the planet.”
The latest series of flight tests on Boeing’s ecoDemonstrator 737-10 began on 12 October and will conclude on 30 October. Initial observations will then be presented to the media later that week.
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Featured image credited to Boeing
