Tests show sustainable aviation fuel produces less fossil CO2 and less particulate matter
Bern, 03.06.2025 — Two years ago, the Swiss Air Force and the Federal Office of Civil Aviation (FOCA) carried out tests on sustainable aviation fuel (SAF) at the Payerne military airbase. These tests confirmed that SAF reduces emissions of soot particles and fossil CO2.
What happens to the ultra-fine soot emissions and volatile particles when SAF is burned? This question was the focus of the tests carried out in spring 2023. They took place on the ground at the Payerne airbase using a Cessna 560 XL Citation Excel, a twin-engine business jet that can carry nine passengers.
Significantly lower soot emissions
A working group of environmental experts from the Zurich University of Applied Sciences, the Paul Scherrer Institute, the Swiss Air Force and the FOCA analysed and evaluated the data. A clear picture emerged: Fossil CO2 emissions are reduced in line with the proportion of SAF in the tanks.
The decline in soot emissions is significant: Depending on the engine configuration, these are up to 35% lower. The reduction is particularly marked when the aircraft is idling - for example, when it is on the ground with the engine running. The reason for this is that SAF generally does not contain any soot-forming aromatic hydrocarbons and therefore burns more cleanly than pure fossil kerosene. It is also sulphur-free. Even with a low admixture, not only are fewer soot particles produced, but also fewer gaseous aromatic and sulphurous substances, which brings an overall reduction in particulate matter pollution and an improvement in air quality.
SAF: Better for the climate and air quality on the ground
Sustainable aviation fuels are a promising approach to reducing fossil CO2 emissions in aviation. Compared with fossil fuels, SAF makes it possible to avoid up to 80% of CO2 emissions without modifying today's engines, including all emissions relating to production and transport. Using SAF is a win-win situation, as it also has a positive effect on the air quality at and around an airport. While similar results were already available for large engines, the tests in Payerne on a business jet engine show that SAF can also be used to reduce pollutant emissions from small engines.
The results of the tests have been published in a scientific journal.
SAF test conditions
The fuel mixture used in the tests contained 35% sustainable aviation fuel (SAF). This met the technical requirements of conventional kerosene. It did not require any technical modifications to the aircraft or the refuelling system. This is important because theseSAF mixtures can be used directly in existing aircraft. The SAF was produced from organic waste such as used cooking oil and animal fats from slaughterhouse waste. In order to be able to compare the SAF mixture directly with conventional kerosene, the right and left wing tanks were filled with different fuels. It was possible to switch between the fuels while the engine was running.
Links:
Bundesamt für Zivilluftfahrt und Luftwaffe testen nachhaltigen Flugtreibstoff
Gaseous and Particulate Emissions from a Small Business Jet Using Conventional Jet A-1 and a 30% SAF Blend | ACS ES&T Air
Alternative Treibstoffe in der Aviatik
SAF-Strategie BAZL
Aviation Infrastructure and Atmospheric Research | ZHAW Centre for Aviation ZAV
Laboratory of Atmospheric Chemistry (LAC) | Laboratory of Atmospheric Chemistry | PSI
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